Recent Posts

1

Projects, Designs, and Technical Stuff / Re: Control of 2 CAN Open DS402 motors on a single shaft

« Last post by moffy on Today at 07:53:47 am »

Just to summarise, to see if I understand correctly, the slave motor is following the torque profile of the master(speed motor) but one sync behind, which is about 3ms, so you should be sharing the load roughly equally and the demand torque to the slave should reduce as the master motor approaches its set speed and its demand torque reduces. It sounds reasonable, what you could do to confirm it is log the current of each motor at the same time and check that they are load sharing during dynamic and static situations. What about when static, no speed change, does the master still provide a demand torque for the slave to follow?

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Beginners / Re: LM324 Power Supply with variable voltage and current

« Last post by mike_mike on Today at 07:53:38 am »

Initial thoughts are, the fans only can be powered from the 2x15Vac transformer.
The tap changer might be able to be powered from the 2x12Vac transformer with modifications so that it can accept negative sensing input voltage.  Because the DVM can only measure positive voltage, it needs to be powered WRT the PSU's negative output. So the unmodified tap changer might as well be powered from the same supply.
 Keep in mind that ground on a Harrison PSU is the positive output.

Can you please be more explicit ? Are you trying to explain that the tap changer could be powered if I modify the schematic ? Regarding the DVM, I didn't understood.

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General Technical Chat / Re: What did you buy today? Post your latest purchase!

« Last post by BennoG on Today at 07:52:13 am »

After refitting the power connector it powered on (verry dim display however).
But when powered off for 2 days it wont power on the first few times and than power on normally.
It looks like the internal 12V and 5V power is in hiccup mode (you can hear it restart)
I have a news display on the way and figuring out why the power supply is in hiccup-mode (overload or component age / fail)

Benno

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Test Equipment / Re: New Zoyi multimeter+oscilloscopes - ZT-70xS, up to 50MHz/250MSps (nov 2022)

« Last post by lchao on Today at 07:49:25 am »

Good Day!

Just want to know if ZT-703S is a good multimeter+oscilloscope for a hobbyist like me.  I am coming from a DSO150.  Which is a better buy among these:

Zoyi ZT-703S ~ 37.80USD (New)
Owon HDS242S ~ 74.16USD (New)
Owon HDS2202S ~ 78.07USD (Used)

At double the price, does the owon variants have better features, accuracy, reliability?


Thanks!

Where did you find these prices? I can find just these lowest prices:
Zoyi 703s shipped to the Philippines is USD 75 on Aliexpress,
Owon HDS242S is USD 144 on Banggood at the moment
Be careful, because sometimes the price os other models are shown if you search for these products (e.g. Zoyi 702 and Owon HDS242 - which doesn't have signal generator)

The 2 products are close to each other in specs, but Owon is double the price. I'm not an electornics expert at all, but based on what I've read so far I found the Owon HDS242S far better than the Zoyi 703s.

Pros for Owon HDS242S compared to Zoyi 703s (for me):
- It seems it has the same hardare as the 70 MHz model, therefore the signal amplitude doesn't shrink even when measuring above 30MHz
- Usable signal generator (Zoyi 703s is very noisy -> low quality, signal output is not BNC)
- Works as described, it meets the specifications
- Has more probe settings e.g. x1000, x10000  (Zoyi has x100 starting since a recent firmware update)
- 4400 mAh battery capacity - 2x 18650 battery (vs. 3400 mAh, 1x 18650 battery in Zoyi)
- Horizontal scale: 5ns/div-1000s/div (Zoyi has 10ns/div-20s/div)
- Stable and accurate software (Zoyi has a lot of inaccuracy issues in the measurements)

Cons for Owon HDS242S compared to Zoyi 703s:
- Has only 8K memory (Zoyi has 128K)
- Multimeter part has "just" 20 000 counts (Zoyi has 25 000)
- It seems firmware is not being updated (Zoyi is continuously gettig FW updates - unfortunately it doesn't mean that all known issues are fixed)
- Somewhat lower bandwidth based on specs: 40 MHz (Zoyi _claims_ 50 MHz, but while you can measure in Owon's full specified bandwidth, with Zoyi's it's not the case)
- Only sold with 1 probe (Zoyi is sold with 2 probes as an option)

All in all I found the HDS far more superior than the Zoyi, but it also comes with an almost 2x price tag.

DISCLAIMER: I have very limited knowledge in electronics. This is solely my opinion and understanding based on the information from manufacturers or elsewhere I found on the Internet. I don't own any of these products.

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General Technical Chat / Re: What did you buy today? Post your latest purchase!

« Last post by beanflying on Today at 07:48:12 am »

Oops I differentialled AGAIN

I really need to get back to my clearance thread but sitting around in boring non Shack/Workshop places with idle hands leads to another Fluke to play with. I already own a better DC only one (895A) but a Fluke 887A AC/DC Null meter will be fun to play with.

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Projects, Designs, and Technical Stuff / Re: Opamps - Die pictures

« Last post by magic on Today at 07:43:37 am »

Nice. This chip still looks quite simple for what it is doing.

This shows that the TLC1051 is not a chopper amplifier but an auto-zero opamp. The signal does not undergo modulation and demodulation. Instead, the current offset value is stored in a capacitor and used for correction, while another capacitor holds the current value of the signal. In addition to the auto-zero path, the TLC1051 includes a parallel path for higher frequencies. This type of opamp is referred to as "auto-zero stabilised".

They describe it as "chopper stabilized" in the datasheet. If you think about it, the part S1, gm1, gm2, S2 is a chopper amplifier: S1 chops the differential input voltage into a square wave, the linear transistors amplify the square wave, and S2 demodulates it back into DC by sampling the peaks. To avoid differential subtraction of peaks and valleys at this point, gm3 works as a DC servo of sorts and ensures that the valleys are fixed near some internal "ground" potential.

The output of the chopper feeds gm4 and gm5, which provide additional gain. And the whole chopper is bypassed at frequencies near the chopping frequency and above in order to reduce aliasing artifacts and achieve GBW much higher than the chopping frequency.

Of course the "auto zero" explanation about gm3 canceling gm1 offset voltage and a bunch of sample-and-hold circuits making it all work is valid too. I'm not sure what the difference between "chopper stabilized" and "auto zero" is supposed to be, and if there is any real difference at all. Maybe it's only marketing talk.

There are three unused bondpads in the lower area. These are additional options for connecting the supply potentials.

It's probably same thing as with MCP6024: two dual dice can be installed together to realize a quad. The top die gets its V+ in bottom left and V- in bottom right. The bottom die is rotated 180° so its supply connections are swapped.

I suppose it works out cheaper than designing a quad die and disabling half of it for the dual

The circuit corresponds to the block diagram in the LTC1052 datasheet. The datasheet states that the amplification factors of the amplifiers gm1 and gm6 must be as equal as possible for proper function. Furthermore, these are the amplifier stages with the high amplification factors. Accordingly, these two sections are relatively large and have the same structure.

These things look like ordinary PMOS differential pairs with PMOS current sources in the middle between gm1 and gm6 and NMOS current mirrors.

Hmm, how far are you from a complete transistor level schematic of this opamp?

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Projects, Designs, and Technical Stuff / Re: Control of 2 CAN Open DS402 motors on a single shaft

« Last post by Simon on Today at 07:37:39 am »

Well if the motors are to sync up and do their thing then all that I can do is have the slave motor provide the same torque as the master speed controlling motor.

So if I send a speed demand in the PDO message and then send a sync message the master will take the new speed demand and respond with a torque target. Now as it stands I don't know if that torque target will be what it was doing or what it is planning to do now that it has the go ahead for the new speed. The sync message basically trigger action on previous commands received (RX PDO) and prompts the sending of up to date information (TX PDO).

So the slave motor will then see the masters torque target as it's torque demand, but it will not act on the demand until it gets another sync message. So at best the slave will be one cycle behind the master unless I can change the settings in the slave so that it reacts immediately to the RX PDO that contains the torque demand.

If the sync message is sent at a much faster rate than the master speed controlling motor can to keep up with any load changes that affect speed then the slave motor will see new torque demands faster than the master is settling at so the action of the slave motor that must be much faster than the master will become part of the masters own control of the speed.

At the moment in dual torque control I am sending sync messages every 3ms but I make a change on every 3rd message to give the motors time to settle before I act on the data and I do that alternately so each motor only makes a change every 18ms. So with this new method that would be the equivalent of sending 6 updates between full control cycles. So I slow down the reaction of the speed controller motor and speed up the reaction of the torque control motor and now that I am doing less processing in my CAN Open master controller I can send the sync message even faster.

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Security / Re: Microsoft repackages apps with a telemetry .NET wrapper

« Last post by Karel on Today at 07:35:15 am »

I would say that Windows is a great modular spyware system which supports some operating system functions 

Yes! This is probably an hyperbole though! MS is only doing this to improve your user experience. Don't you want your experience to be improved?

Yes, I want my experience to be improved. That's why I moved away from ms windows.
Not just at home, also at work (including some colleagues).

9

Manufacturing & Assembly / Re: Brief review of the Zhengbang ZB2520HL reflow oven (T-962A alternative)

« Last post by hp23 on Today at 07:34:46 am »

I have the ZB3530HL & have attempted to use the software provided for the ITECH RF-A350. The software connects ok (the ZB3530HL displays "PC Link" on the LCD). I'm using a USB-Serial lead on Windows 11. When I press "Run" with a suitable configuration, the machine does nothing & the "Now" section at the top shows nothing in the Temperature field. I've tried with flow control & as admin.

I've tried searching for an answer online to no avail. Has anyone been able to get this working successfully & what's the trick?

Pete

10

FPGA / Re: Analog video output with FPGA ?

« Last post by gf on Today at 07:31:15 am »

Should I build a PWM or PDM DAC inside the FPGA ? (in PAL, with 52us per line, 320 columns, 256 possible values and 4 PWM cycles per pixel, that would mean  6gHz clock... probably cheaper to save on the FPGA and use a DAC, but maybe PDM would be doable ?)

Delta-sigma modulation does not need such a high oversampling ratio. A 2nd order modulator with 2-level (binary) output has a theoretical SQNR of ~65dB with 32x oversamling, or ~80dB with 64x oversampling. For 5 MHz bandwidth, this would be 320 MSa/s (32x) or 640 MSa/s (64x). Maybe a little more if you want some headroom, but not 6GSa/s.

See also https://classes.engr.oregonstate.edu/eecs/spring2021/ece627/Lecture%20Notes/2nd%20&%20Higher-Order2.pdf

Edit: How much SNR do you need for analog video? I guess hardly more than 50dB. So even 16x oversampling may suffice, but that's already borderline.

Btw, does the TV have RGB inputs, or do you need a composite video signal?