EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: devttys0 on August 05, 2015, 04:34:21 pm
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After seeing WD5GNR’s work on reversing the serial protocol (https://www.eevblog.com/forum/testgear/mhs-5200a-serial-protocol-reverse-engineered/) for the cheap MHS-5200A function generators, I picked one up off of eBay.
I hadn’t seen much info in terms of how well these units meet their claimed specifications, so I started doing a short review/teardown video, and ended up reverse engineering the analog front end trying to track down the source of harmonic distortion that happens at higher output amplitudes and higher frequencies:
MHS5200A Function Generator Review and Teardown (https://www.youtube.com/watch?v=WfC0h8XhA4w)
TL;DW: it looks like the main issue is that they aren’t providing a large enough supply voltage to the final output stage (an AD812 dual op-amp), and it’s causing clipping/distortion. This is backed up by the datasheet, although it is also clearly a frequency dependent issue.
Here's a schematic (http://www.analogzoo.com/2015/08/mhs-5200a-teardown-and-review/) of channel 1's analog front end (channel 2 is identical) for anyone interested.
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Great video, thanks a lot!
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Very good video. I liked the detailed analysis and the rev eng. schematics.
Thanks and regards
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That was very well done.
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Impressive work getting all the way down to a reverse engineered schematic and building those separate test circuits.
I suspect a lot of the distortion is explained by the slew and current limits of the AD812 amplifier used in the output buffer for the generator. To make a 15 MHz 7.5 V0-p signal you need an amplifier slew rate capability higher than 7.5*2*pi*15e6 = 710 V/uSec. Although the headline slew rate number for the AD812 is 1600 V/uSec that is at +/-15V supplies and optimum feedback resistance. At +/-5V the data sheet lists only 425 V/uSec slew rate for +2 gain. It would not surprise me if at +/- 7.5V and 1K feedback R if the typical slew rate was still less than the required 710 V/uSec.
Note also that the AD812 was design for video with net terminated load R of 150 Ohm. In this generator with 50 Ohm load you are down to only 100 Ohm which means the AD812 does not have enough output current capability before current limiting. See Figure 6. Output Voltage Swing vs. Load Resistance in the data sheet.
For another low cost (< $85) you could consider the FY3224S generator. This one is almost the same as the MHS-5200/MHS-3200. Key differences are 12 bit R, 2R DAC, +/-12V supply, and a better output buffer amplifier. The main drawback to the FY3224S is the current limit of only about 70 mA before clipping. So, 10+ MHz open circuit looks fine up to 20 Vp-p while with 50 Ohm load the current limit clips you to only about 12 Vp-p set point and 6Vp-p across the 50 Ohm load. Still much better than the MHS-5200 result.
See the FY3224S thread for lots more info. A specific MHS-5200 and FY3224S comparison table is given in that thread at:
https://www.eevblog.com/forum/testgear/feeltech-fy3224s-24mhz-2-channel-dds-aw-function-signal-generator/msg697718/#msg697718 (https://www.eevblog.com/forum/testgear/feeltech-fy3224s-24mhz-2-channel-dds-aw-function-signal-generator/msg697718/#msg697718)
gby
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Well, seems like I did the right thing to buy the 12Mhz-Version instead of paying 20€ more for the 25Mhz-Version :D
What I discovered when I powered the unit from my Bench-Supply (Ebay-Seller had sent me a PSU with the wrong type of Plug for European Wall-Plugs) was that the waveforms looked a lot less noisy than when powered with the PSU delivered with the unit. I also measured only 4.75V getting into the unit, suggesting the PSU is not really up to the task.
When I powered the signal-gen with the Bench-Supply, I found a significant improvement on the overall performance when I turned the voltage up to 5.30V (I didn't go higher, as I suspected the 5V-Rail to be directly connected to the PSU): The Display had more contrast and the waveforms didn't seem to flatten at max amplitude.
Also a slight offset of -1 to -2% yielded a much better looking result on the Square-Wave.
Unfortunately, I haven't made any comparison-pictures |O
I am currently investigating upgrading the unit with a battery and an internal switching PSU: The one I got with the unit clearly is not up to the task, but I'm pretty sure one of these cheap chinese Boost-Converter Boards + a 3,7V Lithium-Accu combined with a small charging-circuit connected to the original PSU-Input, will be. And there is more than enough space inside the case to add this.
I also think about modifying the on-board switching regulators to put out +/-15V or +/-12V if the caps are rated for only 16V. If there is nothing else powered from these rails than the AD812, I think this should be possible without risking damage from overvoltage.
The current-draw at 12Mhz, 15Vpp into 50Ohms was about 450mA @ 5,3V btw.
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gby: Yes, the slew rate is almost certainly the problem; the Vpp vs Power Supply issue that I focused on seems to have been a red-herring. After some additional testing and gawking at the datasheet, the slew rate of the final amplifier is probably worse than 400V/uS, much too low. I probably should have guessed that in the first place from the waveform distortion. |O
The most likely reason seems to be that the AD812 is used in an inverting configuration (I'm no expert in current feedback amps, but this seems unusual for a CFA), i.e., a gain of -3. Although the datasheet doesn't mention much for inverting configurations, even a gain of -1 has a relatively terrible slew rate, and I suspect that a gain of -3 could be notably worse.
I re-built the final AD812 stage as a non-inverting configuration, all else being equal (same supply voltage, feedback resistors, etc); from the graphs in the datasheet, a non-inverting configuration should have a much better slew rate. I saw a noticeable improvement in output amplitude (an extra 3Vpp at 15MHz) and distortion which seems to back up the slew rate theory, and I'm in the process of doing a follow-up video.
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I also did some measurements on the Supply for all the components on the board.
The +5V Rail is indeed unregulated inside the unit (directly connected to the PSU-Connector and jumping all over the place between 4.4V and almost 4.7V, depending on Frequency and Amplitude) and the -5V Rail is stable at -4.96V, +9V stable at 9.58V, -9V stable at -9.08V. The 3.3V and 1.2V for the digital circuits are stable too.
In the 12Mhz-Version the Slew-Rate seems to cause only minimal distortion, but the quite significant 10% difference between +5V and -5V-Rail would explain the flattening of the positive amplitude.
The capacitors are all rated for 16V btw. So there shouldn't be any problem increasing the supply-voltage to +/-12V. I haven't found any other component than the AD812 to connected to the +/-9V-Rails.
devttys0: Did you rebuilt the circuit inside the Unit, or did you just built a test-circuit?
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SaabFAN: I noticed that the 5/9V rails not being exactly +-5/9V, but I'm surprised the 5V rail is connected directly to the crappy PS. Well, I guess not *that* surprised.
Not sure if the 10% difference on the 5V rail would cause clipping; the AD603 is the only thing directly in the signal chain that runs off the +-5V rails, and IIRC I measured its peak output at 4.5Vpp, and didn't notice any clipping on its output. I have noticed that there is a positive DC offset error in the final output, which could account for the clipping on the positive half of the waveform.
The slew rate doesn't cause huge distortion at 12MHz and below; I'm pretty sure these units were originally designed for 12MHz max, then they decided to get a bit more money by marketing the same hardware as 25MHz and just updated the firmware.
I just built a test circuit, I didn't modify the circuit inside the unit, though I'm pretty confident they would operate identically as my previous test circuit (which was an exact duplicate of the one in the unit) had the exact same frequency response AFAICT.
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Interesting: Increasing the Supply-Voltage has both increased the max. Amplitude (as well as putting the amplitude out of calibration by about +5%) and the amount of distortion. Before there were only about 13V into 1MOhm possible, now I see 15.6V @ 12Mhz, but also severe flattening and it seems like the Output is either getting saturated or hits the current-limit (dent in the positive going flank, the negative one looks much better). Activating the 50Ohm-Termination increases this phenomenon.
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This is how the Sine-Wave looks right now on my Rigol 1104Z:
(https://www.eevblog.com/forum/testgear/mhs-5200a-function-generator-teardown-review-reverse-engineering/?action=dlattach;attach=165153)
(https://www.eevblog.com/forum/testgear/mhs-5200a-function-generator-teardown-review-reverse-engineering/?action=dlattach;attach=165155)
(https://www.eevblog.com/forum/testgear/mhs-5200a-function-generator-teardown-review-reverse-engineering/?action=dlattach;attach=165157)
Unfortunately, I only have a 75Ohm Terminator right now (50Ohms is on its way).
Strangely, my PM3320A shows different voltages, while the shape on both instruments looks identical. Probably have to recalibrate again. (Which wont yield the best results, considering what I have here: MHS-5200A Signal-Gen and a XR2206 based analog Signal Generator.
So disregard my earlier comments about changes of the amplitude.
I also took some measurements of the square-wave: It has so much ringing, it doesn't even settle at frequencies above 2Mhz.
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Yeah, the square wave overshoot/ringing is atrocious, even at very low frequencies. :-\
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What could the reason be to fail like that at creating a Square-Wave? Too slow slew-speeds?
For comparison: My 74AC14-Based TDR running at 2.432Mhz (RC-Oscillator driving 5 gates with 220Ohm-Resistors to give 50Ohm output-impedance on a not very RF-ish vero-board - no Ground-Plane and components connected with bare wires and solder-"traces" on the bottom-side) vs. the MHS-5200A. Both are pumping their energy into a 75Ohm termination-resistor via a 50cm 50Ohm Coax-Cable. The Signal-Gen is set to 5V Amplitude and 0% Offset.
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The reason this sig.gen. outputs sine distortion on the higher amplitudes and frequencies is because the output op amp(which is possibly a current feedback type) is going into slew rate limiting, which is why you get a triangular wave as the gen. approaches max. bandwidth/amplitude.
Actually, I would expect this kind of gear to be crap, which it is, it's written all over the product.
Why do you guys buy this shit? :popcorn:
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Nice work. Maybe we just need to rebuild the output stage.
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The reason this sig.gen. outputs sine distortion on the higher amplitudes and frequencies is because the output op amp(which is possibly a current feedback type) is going into slew rate limiting, which is why you get a triangular wave as the gen. approaches max. bandwidth/amplitude.
Actually, I would expect this kind of gear to be crap, which it is, it's written all over the product.
Why do you guys buy this shit? :popcorn:
Because it is almost 200€ cheaper than anything similar from Rigol, Siglent, Hantek, etc.
And it meets my requirements: I need an arbitrary waveform-generator to connect to a power-amplifier to simulate a 60W wind-generator.
I had started to build my own Signal-Gen btw. but it proved too time consuming (building everything on Vero-Boards, writing the Firmware and the Software to control the device with the PC).
Despite its shortcomings, this thing is still good value for money in my case (Paid 68€ including shipping for the 12Mhz-Version).
For calibrating my PM3320A I probably have to get something better or find someone with proper Signal-Generators and Pulse-Gens. :)
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I have a different (cheap) unit (MHS-2300A), but I bought it to use in the garage for simple automotive purposes. Mine has floating outputs, decent performance for the price, and works well as a beater generator.
I also have a Rigol DG1032Z and now a Keysight 33522B. These are for bench use.
Different people have different use cases. There is value/good reason for cheap, low-end products. I know you don't like the word "low-end" though :P
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I recently got a GW-Instek 1013 function generator due to Dave's recommendation in one of his videos. Should I have gotten these types of generators instead?
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Because it is almost 200€ cheaper than anything similar from Rigol, Siglent, Hantek, etc.
But there are two options you can take, one is to buy a old skool (XR2206 based) function generator like the GFG-8215A dc-3MHz, alternatively save your money until you can afford AWG like the Rigol DG1022.
The MHS-5200A is simply badly designed :-//
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I recently got a GW-Instek 1013 function generator due to Dave's recommendation in one of his videos. Should I have gotten these types of generators instead?
Yes ways, You did the right thing buying from a reputable make., so how does it perform do you like it?
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wonder if the MHS-5200A shares the same issues as we found in the MHS-2300A (which seems to share very similar design and components).
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Because it is almost 200€ cheaper than anything similar from Rigol, Siglent, Hantek, etc.
But there are two options you can take, one is to buy a old skool (XR2206 based) function generator like the GFG-8215A dc-3MHz, alternatively save your money until you can afford AWG like the Rigol DG1022.
The MHS-5200A is simply badly designed :-//
I already have an XR2206, although only capable to do a little over 100kHz, and the DG1022 was among the devices I was considering (the others were a SDG1000-Series and a comparable unit from Hantek), but they both were priced almost 200€ higher. With this unit I spared me the trouble to figure out all the software-stuff and if I need an accurate amplitude-control, I can still build the amplifier and AGC-circuits I have already drawn up for my own signal-gen.
The digital stuff can probably hold its ground pretty well against the units from the other manufacturers. The problem is the final analog output, which we hopefully can modify enough so it does its job properly.
Besides: With only about 15€ I can make this thing portable (LiPo-Cell, Boost-Converter, Charger + some wires and an additional switch). I doubt this is possible with a DG1022. :D
In hindsight, the FY32XX would probably have been better: 12bit, 50Msps more, twice the waveform-length, more amplitude.
Comparison with the MHS-2300 would be interesting indeed: The analog part seems to be a lot more complicated and incorporates even a few adjustable components.
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SaabFAN: The overshoot/ringing on the square wave output is probably due to the elliptic low pass filter they use on the output of the DAC, but I haven't verified that yet.
commie: I didn't expect it to really be any good. Like I pointed out in the video, there's nothing worse than buying test gear you can't trust. But it is fun to take cheap stuff apart and hack at it, which is mostly why I got one. :)
And yes, the CFA is definitely slew rate limited:
https://www.youtube.com/watch?v=rwn5XnT7NVA (https://www.youtube.com/watch?v=rwn5XnT7NVA)
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Why did they use an inverting configuration in the first place? Is there any benefit to it? Easier to design, issues with DC-Bias, etc.?
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Not sure exactly, perhaps they did it to more easily set the input impedance to the amp, especially for terminating the DAC filter. Seems uncommon for CFAs.
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I just did some reading on the subject: Apparently, only inverting configurations can be used as mixers to properly sum voltages, which, I guess, is necessary in this case to add/subtract an offset from the DAC-Voltage. It is then fed into the variable gain Amplifier, and then again inverted to give the correct output-polarity. Actually not a bad idea, but in this case not up to the task.
What (I think) they should have done: Mix the signals with the first inverting amp, invert the signal again (to have correct polarity), feed it into the variable gain amplifier and then drive an amplifier configured as a non-inverting amp.
Would have added two ICs (or one if one doesn't care about crosstalk too much^^) to the BOM, plus some passives, and required some more space on the PCB.
I guess, this is how they do it on the High-Power Option that is available for these units, which fits in the large empty space next to the PCB inside the case.
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That's true, but I didn't see any summing amplifiers in the circuit. From what I've seen, they achieve the DC offset by adjusting Vref on the non-inverting input of the first AD812 op-amp; I don't see any reason why they wouldn't be able to do that in a non-inverting configuration, but perhaps someone can enlighten me.
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Refitting a Battery and a boost-converter didn't help much, though it appears as if the square-wave at 1 and 2Mhz looks a little bit better...
Installing the Battery was more difficult than anticipated btw. The signal-gen needs about 6A for almost 11ms, before the current-consumption goes down to about 250mA. It can increase up to 800mA with both channels terminated into 50Ohms at 15V and 12Mhz. I therefore had to modify my original circuit quite a bit - First putting in large caps and after that didn't work, I added coils. Now the unit powers on with a 80% charged battery or if the external PSU is connected. I probably could improve that by adding a SuperCap, but I don't have one here and don't plan on buying one specifically for this unit.
I estimate the cost to modify the device in this manner to be about 15€, including shipping.
Attached: Screenshots of my measurements.
All Waveform-Measurements done with 15V Amplitude
Sine-Waves:
Quickprint22 - +15% Offset, 75Ohms
Quickprint23 - 0% Offset, 75Ohms
Quickprint24 - 0% Offset, 1MOhms
Square-Waves: All measurements with 0% Offset
Large Amplitude - 1MOhms
Small Amplitude - 75Ohms
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And here are some pictures of the modified unit + Current-Draw when turning on (Measured with Scope-Probe over the Current-Shunt of my Multimeter, PSU: KA3005P)
Quickprint18: Current-Draw
Quickprint19: Voltage-Drop
The last 2 Pictures show the first, rather clean version of the Battery-Conversion and the quite messy one with all the modifications necessary to make it work^^
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I managed to significantly improve the sine wave distortion and square wave overshoot/ringing with a couple of simple fixes:
https://www.youtube.com/watch?v=-xOKNi8M3xE (https://www.youtube.com/watch?v=-xOKNi8M3xE)
The first was to replace the AD812 with a THS3092. They're pin compatible, but the THS3092 has a much higher slew rate, and I can now output a 15dBm sine wave at 25MHz and the harmonic content is actually within spec (highest harmonic is at -33dBc).
If you look at the attached HarmonicDistortion image, the output of the AD812 is shown in the purple trace, while the output of the THS3092 at the same frequency/power is shown in yellow. The yellow trace is a bit hard to see since it's underneath the purple trace, but you can just make it out; significant improvement!
I confirmed that the ringing/overshoot was caused by the elliptic low pass filter used on the output of the DAC. I replaced it with a Bessel filter designed for a 3dB cutoff at 30MHz, and there's practically no ringing on the waveform. The SquareWave1 and SquareWave2 images show the Bessel filter output on channel 1 (yellow) and the unmodified filter output on channel 2 (green).
The noise level on the output of the Bessel filter is a bit higher when viewed on the spectrum analyzer, especially near the carrier, but it's not too much worse and to be honest the noise performance of this function generator didn't seem to be all that great to begin with. I decided to stick with the Bessel filter for the cleaner square waves, but a Butterworth might split the difference in performance between the Bessel and elliptic filters.
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Nice one, I'm ordering parts right now to try the mod myself :)
I'm curious why they used the AD812 instead of the THS3092 if it is more expensive. Maybe you should send them a link to your videos and show them how it's done (They may even give you their other Signal Gen for free to do some improvements there too :D ).
About my portability-mod: It is unfortunately necessary to use a 20C-Rated Battery to deliver enough PowerUp-Current. Something, I don't know what, loads down the rails and it is not capacitors, because the rails stay pulled below 2.5V even after a minute or so.
The overall price of modifying the unit to be portable is about 15 to 20€, depending on the battery-size. A little bit more if a 7.4V Battery is used because a different charger and a different Wall-Adaptor are required.
A 1000mAh lithium Battery is able to power the signal-gen for about 30 minutes with both channels terminated into 50 Ohms and outputting 1MHz Square-Waves @ 15V. Quite handy to lose yet another cable (Bench-Multimeter is also on Batteries) on my already crowded bench which actually is my Desk that is also occupied by my PC-Monitor and a 4-channel Audio Mixer :D
Would you say that with your modifications, this Signal-Gen has actual value and could be considered a bargain, or is it still highly preferable to spend 200€ more to buy a unit from Rigol/Siglent/Owon with similar/inferior specs in terms of maximum sine-frequency?
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I'm curious why they used the AD812 instead of the THS3092 if it is more expensive
All else being equal (unless I'm missing something), the THS3092 does seem like the better choice here. Given that these units are designed to a very low price point, my guess is that they somehow/somewhere got a really good deal on a large lot of AD812's.
Would you say that with your modifications, this Signal-Gen has actual value and could be considered a bargain, or is it still highly preferable to spend 200€ more to buy a unit from Rigol/Siglent/Owon with similar/inferior specs in terms of maximum sine-frequency?
With or without the mods, I'd say it's still a pretty good deal for the price, just as long as you're aware of its limitations. With the mods its much more acceptable, at least for my needs, but it still has other issues (e.g., square wave jitter is still pretty bad, especially at certain frequencies).
If you want a good, trustworthy function generator, spend the money on a good one (I got an older HP/Agilent off eBay, it's great). The MHS-5200 is useful as a secondary function generator when I need more than one signal, or if I need two phase-locked signals, etc.
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I know it's a more extensive mod, and maybe not do-able without the source code to the micro, but it seems like the output filter stage should be totally removed for square wave output.
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I'm curious why they used the AD812 instead of the THS3092 if it is more expensive
All else being equal (unless I'm missing something), the THS3092 does seem like the better choice here. Given that these units are designed to a very low price point, my guess is that they somehow/somewhere got a really good deal on a large lot of AD812's.
This seems likely if they are also using it in another product.
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I'm curious why they used the AD812 instead of the THS3092 if it is more expensive
All else being equal (unless I'm missing something), the THS3092 does seem like the better choice here. Given that these units are designed to a very low price point, my guess is that they somehow/somewhere got a really good deal on a large lot of AD812's.
or it could be a counterfeit ad812 which they get for a tiny fraction of the price. sorta like all the counterfeit lm2596 out there.
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Nice one, I'm ordering parts right now to try the mod myself :)
Would you (or OP) consider posting a BOM?
I assume the THS3092 is the one without the bottom pad, for example. And the SMD inductors and caps... from the video:
6.5 30 51 and 130pf -- what are those maybe 0402?
And the L are 160, 330, and 560 nH in the same case?
Then 2X everything.
Great job and great video!
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Nice one, I'm ordering parts right now to try the mod myself :)
Would you (or OP) consider posting a BOM?
I assume the THS3092 is the one without the bottom pad, for example. And the SMD inductors and caps... from the video:
6.5 30 51 and 130pf -- what are those maybe 0402?
And the L are 160, 330, and 560 nH in the same case?
Then 2X everything.
Great job and great video!
Looks like a BOM has been posted here http://www.analogzoo.com/2015/08/fixing-the-mhs-5200a/ (http://www.analogzoo.com/2015/08/fixing-the-mhs-5200a/)
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Yup, as krivx pointed out, there's a digikey BOM in my blog post (CSV format, should just be able to upload it to digikey). There are also some more detailed pictures/descriptions of the mods there too.
The caps/inductors I ordered were mistakenly 0402's, while the pads on the board are 0603, so you might want to change them if you aren't comfortable working with 0402 (either size fits on the pads fine).
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Thanks! Yeah I got the gear to do worse, but my eyes probably like the 0603s better ;-)
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I have just finished the mods posted by Devttys0 [http://www.analogzoo.com/2015/08/fixing-the-mhs-5200a]and I just wanted to thank him for this nice improvement. I did order the 0603 size parts because they are easier to work with and fit on the pads better. I have a few before and after mod screen shots below.
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Hey!
Just a quick update on the MHS-5200-A:
A month ago I bought one of these; today I received it and wanted to do these cool mods (thx devttys0 for your great work) but when I opened it I found out that they (the manufacturer) "modified" the Low-Pass filter for the DAC!! |O
This is what it looks like (I didn't change anything!!):
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Hey!
Just a quick update on the MHS-5200-A:
A month ago I bought one of these; today I received it and wanted to do these cool mods (thx devttys0 for your great work) but when I opened it I found out that they (the manufacturer) "modified" the Low-Pass filter for the DAC!! |O
This is what it looks like (I didn't change anything!!):
I received mine about a week ago (25 MHz version) and the output looked pretty nice. So, knowing about the design tweaks and seeing your post, I cracked mine open to have a peek. Lo and behold, mine had been modded at the factory in almost an identical fashion. (There are three solder blobs across the components instead the long line yours has – see attached).
On a side note: for fun, I fed the output back into the counter input. Perhaps unsurprisingly, they don't agree. At 11 MHz, my freshly calibrated receiver (< .1 ppm to 10 MHz WWV on an ICOM 756 Pro-III), showed 5200A output was about 50 Hz off, which isn't too bad. The counter was off a bit more, and in the opposite direction. Though obviously not built as a lab quality instrument, it would still be fun to at least "trim" it and see how it tracks over time. Just something else to fiddle with, which is what all this stuff is for, right? :)
My question is whether anyone has any info on the "internal calibration" mentioned in their manual. I'm hoping there would be another set of commands for calibration, or at least some front panel key press voodoo to invoke it.
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I loaded this new version (link below), connected gen, and tried to do an arbitrary waveform.
Loaded it on "Arbitrary" tab, then wrote to arb00 mem location.
https://www.dropbox.com/s/cdlsuv2w5rkss6g/MHS-5200A_en5.0.rar?dl=0 (https://www.dropbox.com/s/cdlsuv2w5rkss6g/MHS-5200A_en5.0.rar?dl=0)
It shows up on "Control Panel" tab when I select arb00 as wavefom,
but does not output out of the generator.
I need a drink........
Also sweep mode do. And no sweep trigger out of TTL outputs on gen to synch the display
on scope to the sweep. Although I think one could use 2'ond channel to create the trigger
as both channels operate off same time base.
Regards, Dana.
Modify message
« Last Edit: May 01, 2016, 04:19:09 AM by danadak »
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Why not go for the FeelTech FY3224S?
The DA convertor has a better resolution!
https://www.eevblog.com/forum/testgear/feeltech-fy3224s-24mhz-2-channel-dds-aw-function-signal-generator/ (https://www.eevblog.com/forum/testgear/feeltech-fy3224s-24mhz-2-channel-dds-aw-function-signal-generator/)
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I purchased the Ming He last fall.
Still need to get this software to work -
https://www.dropbox.com/s/cdlsuv2w5rkss6g/MHS-5200A_en5.0.rar?dl=0 (https://www.dropbox.com/s/cdlsuv2w5rkss6g/MHS-5200A_en5.0.rar?dl=0)
Regards, Dana.
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My MHS-5200A 25MHz arrived yesterday. When I had a look inside I noticed a modified layout. Somebody knows if the described mods are still necessary or not? I have attached two pictures.
Regards,
Norbert
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Installing the software (rar-file from here) I noticed that its not the MHS-5200a but the MHS-5225a function generator.
Is there any mod for it or are the mods already included there?
Regards,
Norbert
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I just got my MHS-5200A in the mail and it has the redesigned PCB. The THS3092 part number from mouser is it 595-THS3092D? Also, could you use the 595-THS3095D? The slew rate is higher for the 595-THS3095D
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Boy is that square wave ugly..... With the new re-designed PCB...
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That's why you should go for the FeelTech FY3224S instead :)
https://www.eevblog.com/forum/testgear/feeltech-fy3224s-24mhz-2-channel-dds-aw-function-signal-generator/ (https://www.eevblog.com/forum/testgear/feeltech-fy3224s-24mhz-2-channel-dds-aw-function-signal-generator/)
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Boy is that square wave ugly..... With the new re-designed PCB...
It looks like this generator is more for simple hobby applications.
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A couple of days ago I decided for a flash deal at Gearbest's, 51.74$ seemed pretty good to me :)
Obviously they are working permanently on the PCB and I received a fresh new version, although only minor changes.
Maybe manually reworked too, lots of soldering honey in the filter area and numerous soldering spatters.
Unfortunately the CD is mispressed, so no arbitrary for me at the moment, at MHINSTEK I found only chinese program version :((.
(http://abload.de/thumb/pict9969fxux9.jpg) (http://abload.de/img/pict9969fxux9.jpg) (http://abload.de/thumb/pict9970giuhr.jpg) (http://abload.de/img/pict9970giuhr.jpg)
(http://abload.de/thumb/pict99714eue8.jpg) (http://abload.de/img/pict99714eue8.jpg)(http://abload.de/thumb/pict9972nhu1p.jpg) (http://abload.de/img/pict9972nhu1p.jpg) (http://abload.de/thumb/pict9973mau9v.jpg) (http://abload.de/img/pict9973mau9v.jpg)
(http://abload.de/thumb/pict9974b3uw5.jpg) (http://abload.de/img/pict9974b3uw5.jpg) (http://abload.de/thumb/pict9975vbu9z.jpg) (http://abload.de/img/pict9975vbu9z.jpg)
(http://abload.de/thumb/pict9976cpuax.jpg) (http://abload.de/img/pict9976cpuax.jpg) (http://abload.de/thumb/pict99779fuik.jpg) (http://abload.de/img/pict99779fuik.jpg)
Overshoot's still present, ringing cannot tell due to noisy scope...
All waves @1MHz
(http://abload.de/thumb/1mhz_sinedlsuo.jpg) (http://abload.de/img/1mhz_sinedlsuo.jpg) (http://abload.de/thumb/1mhz_sin_ffteesdx.jpg) (http://abload.de/img/1mhz_sin_ffteesdx.jpg)
(http://abload.de/thumb/1mhz_sqqgszv.jpg) (http://abload.de/img/1mhz_sqqgszv.jpg) (http://abload.de/thumb/1mhz_trs1sfh.jpg) (http://abload.de/img/1mhz_trs1sfh.jpg) (http://abload.de/thumb/1mhz_staxs2i.jpg) (http://abload.de/img/1mhz_staxs2i.jpg) (http://abload.de/thumb/1mhz_st_i4hsp0.jpg) (http://abload.de/img/1mhz_st_i4hsp0.jpg)
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Given that these units are designed to a very low price point, my guess is that they somehow/somewhere got a really good deal on a large lot of AD812's.
AD812, AD603, LMH6612, polymer capacitors, dual coil inductors, relays, and probably flash are reused old parts.
But this is actually not too bad considering the price. If they used new parts, it wouldn't be so cheap ($56 including shipping in my case).
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Unfortunately the CD is mispressed, so no arbitrary for me at the moment, at MHINSTEK I found only chinese program version :((.
I've uploaded the software by the following link:
https://www.dropbox.com/s/zjdbeem2rsq5ngq/MHS-5200A.7z?dl=0 (https://www.dropbox.com/s/zjdbeem2rsq5ngq/MHS-5200A.7z?dl=0)
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I, too, have the newer version. I paid about $90 for it because I needed it immediately to run some tests, and had planned to return it and buy the $50 version.
I will post some detailed scope measurements of the signal in a bit, but in the meantime, I figured I'd make use of my shiny new USB microscope and post pictures of all the critical components of this board, so you guys can get a better idea of what's inside. I can post pictures of the overall circuit board later (or you can use the ones above, which are apparently identical to mine). But none of the previous photographs have quality IC pictures, so I figured I'd contribute.
Although uploading 25 images on this forum is kind of tedious...
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I continue in this post...
There are "missing" pictures above, but they were just deleted bad-quality duplicates. Fear not, no parts are missing.
edit: Evidently my rotation settings didn't save. Sigh. I give up.
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Measurements of the newer-style MHS-5200A.
Test Conditions:
- both devices reset to default settings
- connected directly using 50-ohm (verified) BNC to BNC cable
- Rigol 1054z with 1x setting
Test 1:
- Control: 2.100 kHz (a reasonable minimum)
- Variable: 1, 5, 10, 15, 20 Volts
- Measuring: Rise Time, Overshoot, Vpp
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Measurements of the newer-style MHS-5200A.
Test Conditions:
- both devices reset to default settings
- connected directly using 50-ohm (verified) BNC to BNC cable
- Rigol 1054z with 1x setting
Test 2:
- Control: 1 Volt peak-to-peak
- Variable: 40, 50, 60, 70, 80, 90, 100, 170, 180 kHz then 2.0 MHz
- Measuring: Fall time, picture
Bonus:
Whatever is going on here, animated.
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Measurements of the newer-style MHS-5200A.
Test Conditions:
- both devices reset to default settings
- connected directly using 50-ohm (verified) BNC to BNC cable
- Rigol 1054z with 1x setting
Test 3:
- Control: 6.0 MHz (the fastest frequency which doesn't totally look like a sine wave)
- Variable: 1, 5, 10, 15, 20 Volts
- Measuring: Rise Time, Vpp, Overshoot
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I wish we had the firmware to play with. Also anyone probe the pads on the circuit board? On the side. I like the unit. I just wish it had better performance.
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I just bought new one for 50$, as previously reported it does seem to be improved from the original terdown. I know the limitations of my new toy and so far I'm very happy with the purchase (performance / price point).
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I've uploaded the software by the following link:
https://www.dropbox.com/s/zjdbeem2rsq5ngq/MHS-5200A.7z?dl=0 (https://www.dropbox.com/s/zjdbeem2rsq5ngq/MHS-5200A.7z?dl=0)
thx, I found it in the meantime on MHInstek website.
Installed and running fine so long.
I wonder about the efforts with excel sheets and export stuff from alternative Software, I have nothing to complain at the moment.
GB did a refund about 25$ plus 125 extra points(2$50).. so no bad deal. :-DD ;D
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For those interested, I finally got a hold of one of the new MHS5200A units and did a short overview of the new features, plus a teardown, circuit analysis, and performance review.
https://www.youtube.com/watch?v=TQXd7u4kPvs (https://www.youtube.com/watch?v=TQXd7u4kPvs)
TL;DW: The analog front-end underwent a not-insignificant redesign. The newer models generate much nicer square waves, at the expense of increased high frequency noise. Slew rate distortion is still an issue. Generally poor performance when compared to a "proper" signal generator, but for the price it's still a good bang-for-the-buck, especially if you're only interested in lower frequency signal generation and don't mind the HF noise in the output signal.
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I watched that video last night. Prolly good enough for my needs.
I missed the part whether this can do a sweep or adjust frequency via dial on the fly, or if needed to be paused/stopped to adjust.
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Thanks for the video. I'll try the 100pf cap....
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Ah crap! I just bought one of these (newer 12bit model), but didn't realize I was buying the 6 MHz version instead of the 25 MHz version (was $1 cheaper). Doh! |O
According to this manual I stumbled across, the only difference between models is the Sine way frequencies (all other generators seem capped at 6 MHz). Has anyone looked in to dumping/reprogramming the firmware yet? I would imagine they're exactly the same, just different firmwares.
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I bought a MHS-5225A release R5.04
started to play with and found following "challenges":
1) Frequency Error
- connect "In ext." with "ch 1"
- set frequency to 20.000 000 00 MHz
- run the internal frequency counter with 10s gate time
-> my result is 20.000 146 3 MHz (7.3ppm deviation)
Interpretation:
- crystal frequency error is factory calibrated (my 7.3ppm are a device specific value)
- DDS-generator is frequency corrected, frequency counter is not corrected
2) Frequency Resolution
- expected 10mHz resolution at any frequency
- use the setup for "Frequency Error" and try to set the frequency in a way that the
counter is showing 20.000 000 0 MHz
-> you will find that the frequency resolution is in the range of 1...5Hz (in an irregular fashion)
Interpretation:
- frequency correction is running into numerical issues
- required number of discrete frequencies is 25MHz/10mHz = 2.5 x 10e9
would nicely fit into 32bit unsigned integer
- my gut feeling
frequency correction is using 32bit floating point format (with 25bit mantissa)
-> missing 7bit -> 10mHz x 128 = 1.3Hz b.c. resolution @ max. frequency
3) deterministic square wave distortion
- set generator to 1kHz square wave
- connect a scope, trigger on falling edge
- zoom in (e.g. 1us/div)
-> you will observe a very surprising distortion!
a small "bonus step" 1us in front of final falling edge
height of step is approx. 12% of pp signal amplitude
length of distortion is a function of frequency (approx. 0.001 * 1/f)
Interpretation:
I have no glue !!!
4) temperature of output driver ICs (at least for the replacement type)
- they are really hot!
-> strongly recomment to invest in a bigger heat sink and a small amount
of thermally conductive paste
My general impression:
good enough entry level product at an attractive price point
(even with the known impairments)
Have Fun !
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With just R2R resistors at the FPGA output, is there a really improvement going from 8 to 12 bit - even the 8 Bit are difficult to get right. So how does a lower frequency triangle look like ?
The slew rate limit is not that bad for a sine wave. Reducing the amplitude at the highest frequencies is not such a bad restriction. It is more a problem to the square wave, but here using just an NCO there is a lot of jitter anyway. So not a good square wave anyway. A good square wave would need a filter and comparator.
Wondering why the use the extra AD8017 and still the AD812 for the output. They could have used the same OPs for both function. Likely the AD8017 would be slightly better for the output stage as well.
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I posted this same reply on the other relevant MHS5200A teardown/hack thread, but thought I would post here for those not in the other thread...sorry for the spamming haha.
I know im late, but thought I would put in a word about some scripts im developing to further gain access to the MHS5200A device via serial commands. Namely, I have started with a dumb script that asks it for the frequency (on "EXT_IN") once a second and plots it in gnuplot. Links to the github repo and a boring video of me using it below. Let me know what needs fixed!
NOTE: I compile and run on Ubuntu, should work on other Linux distros, as for Windows and hackcoughblechApple there is work to do still obviously...
https://github.com/electricsheeplabs/mhs5200aDataLogger (https://github.com/electricsheeplabs/mhs5200aDataLogger)
https://www.youtube.com/watch?v=aVf_DMRtWCs&t=60s (https://www.youtube.com/watch?v=aVf_DMRtWCs&t=60s)
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Hi, I have a question, what is the maximum continuous current (square wave 100%) that supports the equipment ?? Can be used as DC source for Arduino or Raspberry Pi 3 ??
Thanks
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Hi, I have a question, what is the maximum continuous current (square wave 100%) that supports the equipment ?? Can be used as DC source for Arduino or Raspberry Pi 3 ??
Thanks
No way. It's something like 20 to 30 mA. Even if that's off, it's still a few orders of magnitude too little current.
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Ok thanks, I was not aware that it supplied so little current.
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Hi all,
New to the forum and first post here. Recently ordered MHS-5200A. I am not an expert of the electronics. Learning my way through the jungle of electronics here.
I have a noob question to this forum, can you generate an AM wave using MHS-5200A? If yes, can you explain how?
Thank you.
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I think your options are arbitrary wave function output (so it would be a fixed AM wave you create) or mixing two outputs, one being carrier and the other is signal... so the answer is "no", but also yes.
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guys I have had this tool for a few years and I would like to change the chips to improve the output signal, I show you some photos of the interior because in my model there is a dissipated voltage regulator complete with a cooling fan.
the external power supply is a 12v. 3A. that arrives in this internal regulator which then supplies the voltages to the device.
instead the two chips of the first and second channel have to be changed, besides I don't see any filter like in your photos, what do you think?
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another photo...
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rear side, as you can see, there are the channels output, ch1 and ch2