Recent Posts

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Projects, Designs, and Technical Stuff / Accurate sine wave in terms of amplitude

« Last post by sw_guy on Today at 08:05:26 am »

I am iterating options to generate accurate sine wave in terms of amplitude. Absolute frequency is not critical in this application.
There are few options and the first in my mind was AGC controlled wien oscillator. The main factor is temperature. Since the AGC is based on diodes, the "accuracy" of the circuit below is not even on the right map.


Another option is to use AD9833 (or equivalent) waveform generator chip. There might be better options in terms of amplitude accuracy, but the chip in question looks like be able to keep amplitude within 0.3% between 25 and 50C.

In practice, generating square wave accurately (still talking about amplitude) might be the easiest. Then it is matter of filtering to get sine wave. (and this time taken into consideration temperature impact to resistors and capacitors).

The target is to have 0.1% accuracy. To get there I am expecting to have stable enough generator + calibration.

sw guy

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FPGA / Re: Analog video output with FPGA ?

« Last post by Jaunedeau on Today at 08:03:36 am »

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 oversampling, 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

Thank you. My calculation was for PWM, I'm just trying to learn about PDM for my application and can't do the math yet. If 32MHz is enough, that might be done with SPI on a cheap STM32 or the PIO or an RP2040 and that would greatly reduce cost. But my understanding of PDM (and that would almost be the same problem with PWM) is that if I want to display a full 1/256 brightness line with a 16 oversampling, I would display first pixel as 1 followed by 15 zero, followed by 15 pixels all black (full zeros), making an average of 1/256, but meaning I would need a filter that averages the value over 16 pixel. I'd still get good micro adjustements if I output analog source or video from a camera (hence I don't need 256 oversampling for them), but in my case (pure digital source whed having a 1 pixel wide white ball on a black background is not uncommon) PDM won't be really better than PWM ? (and PWM would still need at least 2x oversampling, or alternance and black and white pixels would be hard to distinguish from continues line of mid-gray pixels) ?

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.

I don't now how to answer that question. I want a "clean" rgb video output for a very arbitrary definition of clean ^^

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

I an targetting TVs (and maybe later computer CRT monitors) that have RGB input only

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FPGA / Re: Analog video output with FPGA ?

« Last post by SiliconWizard on Today at 07:59:25 am »

Well, are you sure you need 24-bit RGB to drive an old CRT TV anyway? I am not.

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Repair / Re: Mig welder wire feeder controller board not working

« Last post by .RC. on Today at 07:58:26 am »

I believe I have found the problem.  Could not work out why I could not get any of the DC voltages anywhere and why I could not get continuity to the isolation transformer from one of the AC input legs.  So I suspected it was a power supply issue.

Removing the isolation transformer revealed the problem.

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Microcontrollers / Divide clock by 3 on a ATF16V8B

« Last post by Boomchil on Today at 07:56:48 am »

Hi everyone.

I would like to divide a clock by 3 using an ATF16V8B, to clean the video signal of a Sega Master System 2 (to bypass the division made internally which creates noise in the RGB lines). I only have ATF16V8B and I'm struggling to find the code or even the tools to do it (I'm on MacOS).

I have found this VHDL code : https://www.asic-world.com/code/vhdl_examples/divide_by_3.vhd so far but I can't find the tools to synthesis it to Jedec.

Can you please tell me if this is doable, and how could I do it ? I can access to a Windows computer if needed.

Many thanks for your help 

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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.