Author Topic: Hacking the Siglent SDM3055 Bench DMM  (Read 3789 times)

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Offline tv84

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #25 on: August 17, 2019, 12:32:49 pm »
I've successfully running the remote debug using Texas Instrument Code Composer Studio...

Must study that.   :clap:
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #26 on: August 18, 2019, 05:39:42 pm »
I've done a very long measurement to check the quantification level.
All measured values are using 22.5bits (slow mode or 4.7SPS). There's no loss during calculation.
22.5 bits corresponding to 6.77 digits. A full 24bits ADC (as seen in the SDM3065X) could provide 7.2 digits.
A long integration time with a sinc filter could provide more bits.
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #27 on: August 19, 2019, 07:48:41 pm »
I need your help, and I've added 2 questions on the first post :
https://eevblog.com/forum/testgear/hacking-the-siglent-sdm3055/msg2605347/#msg2605347



I've done multiple meaures with an AD584 at 2.5V with 7.5 digits.
- Statistic averaging of 500 samples give 2.496551V
- Averaging of 23 values in 5 seconds give 2.49655078V
- Sinc filter of these 23 values give 2.4955098V

measurements of a 10K 0.1% 30ppm resistor with 7.5 digits
- Statistic averaging of 500 samples give 10.005007k
- Averaging of 23 values in 5 secondes give 10.0050084k
- Sinc filter of these 23 values give 10.0050086k
- Statistic averaging of 4k samples give 10.005006k


The noise level during A/D conversion is very low in Resistance mode (much more lower than DCV).
« Last Edit: August 19, 2019, 07:52:03 pm by alexvg »
 

Offline maginnovision

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #28 on: August 19, 2019, 08:09:23 pm »
Are you comparing what you get to something that is actually more accurate, or are you just assuming this is giving you relevant data(not noise)?
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #29 on: August 19, 2019, 10:27:56 pm »
Are you comparing what you get to something that is actually more accurate, or are you just assuming this is giving you relevant data(not noise)?
Actually I trying to identify all most important noise sources (ADC, Voltage ref, op-amp, relay...).
I measure the distribution of data to see if internal processing maintain all available bits (from ADC).

The SDM3055 PCB analog-part is the base of the 4.5 and 6.5 digits DMM and I think it could be go to 7.5 digits (but with another ADC and some addtitionnal important modifications).
I don't know if 7.5 digits could be really possible with less minor modification, but I'm currently working on these little hardware modifications to check that (with software modifications and/or new software).
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #30 on: August 20, 2019, 08:47:08 pm »


Would you agree to pay a small amount for a new SDM3055 software (and maybe for the SDM3045) ?
http://www.pixule.com/39863606081_would-you-agree-to-pay-small-amount-for-new-sdm3055-software-and-maybe-for-the-sdm3045.html

Would you like to improve your SDM3055 by adding a some options ? (The SDM3045 may be compatible with these options.)
http://www.pixule.com/398636486944_would-you-like-to-improve-your-sdm3055-by-adding-some-options.html

Thanks for your help !
Sorry for double-post.
 

Offline tv84

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #31 on: August 20, 2019, 08:51:51 pm »
That's a wrong move!
 

Offline maginnovision

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #32 on: August 20, 2019, 09:05:15 pm »
You start charging and you might be asking Siglent to challenge you. Since you're modifying their firmware it could be a legal issue.
 

Offline joeyjoejoe

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #33 on: August 20, 2019, 11:10:07 pm »
Asking for something to go wrong. Anyone needing more resolution would probably spend on the 3065 for supported 6.5 digits. Only hacker community would entertain this, and these are the folks who wouldn't pay for something like that.
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #34 on: August 20, 2019, 11:20:01 pm »
You start charging and you might be asking Siglent to challenge you. Since you're modifying their firmware it could be a legal issue.
That's not what I want.
My first tests was only done for evaluation only, I don't want to bother Siglent (I appreciate theirs products !).
I prefer providing my own firmware (not related to Siglent) but compatible with their product while offering additionnal, new or different features.
The SDM3055 is very good, I think it could be even better. My goal is to maximize this device.

Asking for something to go wrong. Anyone needing more resolution would probably spend on the 3065 for supported 6.5 digits. Only hacker community would entertain this, and these are the folks who wouldn't pay for something like that.
You could be right... In the Android community some people are ready to pay some OS updates and advanced features for their old device. The SDM3055 is an old device.


I really appreciate your help, yours advices and opinions. Thank you.
« Last Edit: August 20, 2019, 11:26:29 pm by alexvg »
 

Offline maginnovision

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #35 on: August 20, 2019, 11:35:55 pm »
As far as I can see the 3055 is not old, it's a current product.
 

Offline blacksheeplogic

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #36 on: August 21, 2019, 12:26:42 am »
You start charging and you might be asking Siglent to challenge you. Since you're modifying their firmware it could be a legal issue.

OK, just so I have this straight. It's OK to steal but no OK to charge for stolen items? I was obviously under the misunderstanding that both were wrong.

If your providing a patch to 'extend' functionality (your own work, not enabling someone else work) to a device not sure where the legal issue comes from (sold or given). If your providing FW that's been patched which includes the original FW that's quite different as you are giving/selling someone else work.
 

Offline maginnovision

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #37 on: August 21, 2019, 12:43:01 am »
You start charging and you might be asking Siglent to challenge you. Since you're modifying their firmware it could be a legal issue.

OK, just so I have this straight. It's OK to steal but no OK to charge for stolen items? I was obviously under the misunderstanding that both were wrong.

If your providing a patch to 'extend' functionality (your own work, not enabling someone else work) to a device not sure where the legal issue comes from (sold or given). If your providing FW that's been patched which includes the original FW that's quite different as you are giving/selling someone else work.

Both are wrong, but if you're charging people are more likely to take notice. It's not open source software, modifying it could be illegal.

To add some context Keysight Daniel bogdanoff once said they don't care if you hack your scope but they do care if you try and sell hacked scopes.
« Last Edit: August 21, 2019, 01:14:23 am by maginnovision »
 

Offline Mr. Scram

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #38 on: August 21, 2019, 10:13:08 am »
Both are wrong, but if you're charging people are more likely to take notice. It's not open source software, modifying it could be illegal.

To add some context Keysight Daniel bogdanoff once said they don't care if you hack your scope but they do care if you try and sell hacked scopes.
He's saying he'd provide his own firmware not related to Siglent. Writing your own firmware and selling it is fully legal but not trivial to pull off.
 

Offline coromonadalix

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #39 on: August 21, 2019, 10:39:04 am »
Is it me   or its going in the wrong direction ?   even if he provide his code,  where the code base came from ? Siglent   no/yes ?
 

Offline Mr. Scram

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #40 on: August 21, 2019, 10:42:53 am »
Is it me   or its going in the wrong direction ?   even if he provide his code,  where the code base came from ? Siglent   no/yes ?
Apparently not. Writing your own code completely from scratch is legal. Patching existing firmware with your own code also tends to be legal as you don't copy or provide someone else's code.
 
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Offline JohnG

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #41 on: August 21, 2019, 01:52:37 pm »
This is really nice work, and the related discussion interesting as well.

But, there is a practical matter. A modified meter will have no warranty and reduced odds of support. Have you checked the prices of used 34401 meters lately? Not as many modern features as the 3055A, but they use a LM399 reference and do 6.5 digits without mods. The reference has a good chance of being aged and stable.

I have both meters. The 3055A is easier to use, for sure, but not much of a track record regarding accuracy. A modified version, even less so.

Just my $0.02.

John
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #42 on: August 22, 2019, 09:23:16 pm »
Is it me   or its going in the wrong direction ?   even if he provide his code,  where the code base came from ? Siglent   no/yes ?
The SDM3055 is based on Linux operating system with only a binary file written (partially) by Siglent launched during startup. Used internal libraries and all external libraries come from Texas Instrument, Linux system...

As far as I can see the 3055 is not old, it's a current product.
It's an old device from 2014... Lots of units have been sold : maybe some people would be interested in updating or improving their device without buying a new more powerful and perhaps more expensive DMM.
« Last Edit: August 22, 2019, 09:36:58 pm by alexvg »
 

Offline NoisyBoy

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #43 on: August 23, 2019, 01:19:20 am »
Since you are trying to build something to sell, I doubt this is an appropriate discussion for this forum especially when you try to do a product interest survey. 

The 3055 is not designed as an open hardware platform for open source firmware development.  I will never pay for “enhanced” firmware that does not come from the manufacturer, it is a sure way to void the warranty plus I will never trust the reading. 

I am not saying it is a bad idea, just that it is more appropriate to be discussed in another venue.
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #44 on: August 26, 2019, 07:10:36 am »
Thank you for this very interesting and informative discussion.

About software, I'm continuing working on the new firmware :
- I've successfully access to the display and keyboard.
- I'm waiting for the Lattice USB programmer.
- I'm currently investigate the protocol between digital and analog boards.

About hardware, I've received the components to build a pre-regulated power supply.
I'm waiting for the LTC6655BHLS8-2.5 voltage reference. I'll try one chip to measure ADC noise.
I'd like to build a 6-chip voltage reference : 6x LTC6655 in parallel to limit noise and deviation.
I'm waiting for a brand new calibrated voltage reference (based on the LM399AH).
I'm always searching for a calibrated LTZ1000ACH voltage reference module, I could not find it. Any ideas ?
« Last Edit: August 26, 2019, 11:09:22 am by alexvg »
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #45 on: August 30, 2019, 04:22:37 pm »
I've found some interresting things :
- Only low-23 of 24 bits are used in the software (the 24th bit is used as a polarity bit - shame)
- I've done some precision simulations using datasheet ADC and I presume the ADC used have an internal precision of 24bits (instead of probably 32bits ADC used in the SDM3065X). Using software filtering and fast ADC sampling rate, it's seems to be possible to have a some better results.
- I've found some better Op Amp at the same price (ADA4528-2 instead of AD8629 and LTC1151 instead of AD706)
- I've received a LM399AH-based voltage reference calibrated at 10.00000V (my SDM3055X displays up to 10.001V)
- Resistance measurement (2 or 4 wires) is more stable than current or voltage measurement.
- The internal +5V, +15V and -15V have some 100Hz (from 50Hz AC).

« Last Edit: August 30, 2019, 06:54:56 pm by alexvg »
 

Offline Kleinstein

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #46 on: August 30, 2019, 08:04:01 pm »
It is kind of normal that 1 bit is used for the sign. So 23 bits + sign is kind of normal. Chances are the noise of the ADC is high enough, that there is very limited value to more resolution. With long time averaging a slightly high resolution can be possible, but this does not need the numbers from ADC chip itself.

The ADA4528-2 OP is not per se better than the AD8629 - they are different:  the ADA4528 is very low voltage noise, but higher bias and much higher current noise. The ADA4528 is good for signal sources with less than some 10 K impedance. However the AD8628 is much better for high impedance sources, like the input divider for the higher voltages.

In case one really want's to get sub 100 nV resolution, it would be more like an extra external preamplifier based on an OP like ADA4528. This could also add more gain and have a higher precision protection part (though possibly lower maximum voltage, more bias). Chances are in the lower cost meters the protection is just a resistor, maybe PTC. This could add enough resistance and noise so that it does not make sense to use the ADA4528.

Similar the LTC1151 and AD706 are good for different applications. So it depends on the use. AZ OPs can add quite some spikes, that might upset other circuit parts.

If resistance measurement is more stable than voltage and current measurements, this indicates that the reference noise is a mayor contribution. This might also be the external reference. A lower noise reference may be one of the few actually possible hardware mods, especially if the reference noise is really that bad. Usually the voltage readings near 0 V should be not effected by reference noise, but a reading near to the full scale (e.g. 2 V range, maybe 20 V range) should.

The chip SD ADCs are usually more like good for the lower end 6 digit meters, as the INL can be relatively high. The other problem is the limited range, so that there can be additional gain errors from resistors. So one may get more resolution (low enough noise), but the accuracy is still limited. These SD ADC chips are good for 5.5 digits, and they can even have a good point: the bandwidth for the input noise can be low, as they may not loose time to AZ phases.
 
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Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #47 on: August 30, 2019, 08:25:57 pm »
Kleinstein> Thanks for your very interresting post !!!

I've intercepted data from the FPGA to get the used protocol.
Now I could convert the raw value into voltage value using the DMM calibration XML.

I've detected the real range of the analog input (VDC mode) :
- 200mV range : -312.33mV to +312.55mV (without ADC overflow)
- 2V range : -2.4984V to +2.5110V (without ADC overflow)

In VAC mode (100Hz sine)
- 2V range : 0 to +5.0356V (without ADC overflow)

Measurements done using Rigol DG4102 (as a DC voltage generator) and UNI-T181A (as a voltage measurement)

The VDC mode uses 23bits and 1bit for the polarity (sign)
The VAC mode uses 24bits but within a range from 2^23 to 2^24-1 (like 23bits)
The resistance mode (2W and 4W) uses the same limitation as VAC mode (23bits)

I'm also working on 2 mods in parallel : power-supply low-noise preregulation (plug and play) and multiple LTC6655BHLS8-2.5 chip for the voltage reference (need soldering).
« Last Edit: August 30, 2019, 09:10:30 pm by alexvg »
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #48 on: August 31, 2019, 02:58:58 am »
It was hard to do but now I could access to ADC raw data.

Done :
- Read keyboard state
- Access to display
- Read ADC raw data

To do :
- Control capture mode
- Speaker
- External trigger
- VMC Output



 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #49 on: August 31, 2019, 08:20:08 pm »
I've done the investigation of the 20V VDC range... It's very funny :
-31.25V to +31.25V (without calibration)

 


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