Brymen BM257s DIY PC datalogging USB cable

[lukino]

Hi everyone!
I was following this forum for a long time when I was searching for the right multimeter for me, and thanks to it, finally I have found a Brymen BM257s on TME.eu and I decided to order it.
I received my multimeter today and I immediately started to search a way to make a DIY cable to do some datalogging.
Here are my few attempts, using a FT232RL USB-UART converter (BM257s does not require polling, so I'm focusing on RX):
- Putting a photodiode across GND and RX pins using a pull-up resistor OR putting a photodiode across VCC and RX pins using a pull-down resistor (see attachments).
- Putting an IR receiver (the one with 3 pins) with signal line tied to RX pin (see attachments).
I can see activity led blinking and i can get the output from a terminal, but all the software I tryed didn't work: sigrok-cli, qtDMM, and also official Brymen software.
At this point the problem should be my cable, since even official software doesn't connect.
I will update this post soon with more details!
Cheers!

Update: see attachments

[retiredcaps]

I will update this post soon with more details!

Yes, please do.   

[Flenser]

i can get the output from a terminal

The sigok wiki lists the Brymen BM257 as being supported:
http://sigrok.org/wiki/Brymen_BM257

If you can get output on a terminal then you should be able to check the serial output you are seeing against the Brymen protocol description to confim if your cable is working:
http://www.brymen.com.tw/product-html/software-download/Protocols/6000-count-digital-multimeters-r1.pdf

Good luck!

[lukino]

i can get the output from a terminal

The sigok wiki lists the Brymen BM257 as being supported:
http://sigrok.org/wiki/Brymen_BM257

If you can get output on a terminal then you should be able to check the serial output you are seeing against the Brymen protocol description to confim if your cable is working:
http://www.brymen.com.tw/product-html/software-download/Protocols/6000-count-digital-multimeters-r1.pdf

Good luck!

I know sigrok supports BM257 but the terminal I mentioned was a serial one, sigrok doesn't find the DMM. Same thing happens with official software.
The serial output (in HEX, as the protocol PDF reports) is something like that in the attachments:

[Redeeman]

I think you might be having a problem with the IR reciever.

I have just made a connector like this myself (well... final build is not quite finished), and what i can tell you is:

the specific IR phototransistor/diode matters a lot.

I have a bunch of 5 and 3mm diodes from aliexpress that just says "940nm" and they have IR filter.

stuff them into the back of the BM257s, and yeah, they pick up, the signal isnt too perfect, but the it semi sorta works, but its EXTREMELY flimsy as far as the "correct" signal being picked up, move the diode half a millimeter and everything goes bust.

What I have found to work, is using a 5mm phototransistor, I should note though, that the 5mm phototransistors dont seem to turn fully on with the signal, whereas the 3mm does. it does however give me around 500mV output. This is not enough to provide TTL high, so i have abused an lm358 as comparator with a voltage divider set to 226mV.

the output of the IR transmitter in the bm257s is as you have guessed very conveniently uart that you can put directly to an ftdi/similar or input on arduino.

I will find up some photos and post today


edit/update:
i looked at your hex dump, i doubt you're getting a correct signal here. the bm257s sends a reading as i recall every 200ms, and the first byte is always 02. What i recommend is that you set the meter in ohms mode and short the leads, that way you should always be getting the same series of 15 bytes repeatedly. if you dont, something is definitely wrong, if you do, it can still be wrong if the photodiode/transistor you use is a bit funky or angled wrong or such.

also btw, a huge thanks to eevblog member "jadew" for helping me with this

[lukino]

I think you might be having a problem with the IR reciever.

I have just made a connector like this myself (well... final build is not quite finished), and what i can tell you is:

the specific IR phototransistor/diode matters a lot.

I have a bunch of 5 and 3mm diodes from aliexpress that just says "940nm" and they have IR filter.

stuff them into the back of the BM257s, and yeah, they pick up, the signal isnt too perfect, but the it semi sorta works, but its EXTREMELY flimsy as far as the "correct" signal being picked up, move the diode half a millimeter and everything goes bust.

What I have found to work, is using a 5mm phototransistor, I should note though, that the 5mm phototransistors dont seem to turn fully on with the signal, whereas the 3mm does. it does however give me around 500mV output. This is not enough to provide TTL high, so i have abused an lm358 as comparator with a voltage divider set to 226mV.

the output of the IR transmitter in the bm257s is as you have guessed very conveniently uart that you can put directly to an ftdi/similar or input on arduino.

I will find up some photos and post today

It would be a great help if you have some photos!
I was wondering about the too low output of the photodiode, I'll try to put a transistor or an op-amp to enhance the signal.

Thanks to everyone for the replies!

[Redeeman]

i attempted using a bc547, didnt work but yeah, will definitely post pictures.

i can also give you the part number of the phototransistor i have ended up using, it was bought from TME, i bought a handful of different ones, and i have found some to be unsuited for this, and some that works, albeit with a log signal that needs fixing

[lukino]

i attempted using a bc547, didnt work but yeah, will definitely post pictures.

i can also give you the part number of the phototransistor i have ended up using, it was bought from TME, i bought a handful of different ones, and i have found some to be unsuited for this, and some that works, albeit with a log signal that needs fixing

So, what multimeter are you using with your cable?

[Redeeman]

okay a few photos

note that it, on those photos, runs off a 9v battery, the ~226mV voltage divider was calculated for 5v for an AVR, but it works regardless.

the phototransistor i use is liteon LTR3208 or "IRE5", for some reason it has now disappeared for sale from TME, old link was:
http://www.tme.eu/en/details/ire5/transmitting-and-receiving-ir-elements/liteon/ltr3208/

I also have decent luck with Kingbright electronic L-53P3C and L-53P3BT, the latter has IR filter and is blue.

I have shown you how i put a bit of heatshrink over the phototransistor, this particular one is an L-53P3C but the one in actual use is the IRE5/LTR3208. I initially did it to try shield for light from the outside, I have since found that this does not seem to be required, but it doesnt hurt, and since the IRE5 does not have IR filter, i just left it.

You can see the scope decodes the rs232 signal both on the feint output of the phototransistor and the "clean" signal coming from the lm358

[Redeeman]

and one more due to size restrictions

and on imgur for high resolution:
https://imgur.com/a/8Q6a6

[lukino]

okay a few photos

note that it, on those photos, runs off a 9v battery, the ~226mV voltage divider was calculated for 5v for an AVR, but it works regardless.

the phototransistor i use is liteon LTR3208 or "IRE5", for some reason it has now disappeared for sale from TME, old link was:
http://www.tme.eu/en/details/ire5/transmitting-and-receiving-ir-elements/liteon/ltr3208/

I also have decent luck with Kingbright electronic L-53P3C and L-53P3BT, the latter has IR filter and is blue.

I have shown you how i put a bit of heatshrink over the phototransistor, this particular one is an L-53P3C but the one in actual use is the IRE5/LTR3208. I initially did it to try shield for light from the outside, I have since found that this does not seem to be required, but it doesnt hurt, and since the IRE5 does not have IR filter, i just left it.

You can see the scope decodes the rs232 signal both on the feint output of the phototransistor and the "clean" signal coming from the lm358

Thank you for your help! I hope to be back soon with good news!

[Redeeman]

no problems, if theres anything i can help with just let me know

[lukino]

no problems, if theres anything i can help with just let me know

Good news, I managed to get working the serial port, let me do some tests and I'll post the results!

[lukino]

Here are my results:
- Using a lm385 to enhance the signal solves the problems with serial communication (thanks Redeeman!)
- Official software works through wine, just linked serial port in the wine prefix, but as expected it has a slow update rate (also on windows).
- Sigrok now finds and reads the output from the multimeter, sigrok's protocol could be enhanced but this way I can get about 8 samples per second as opposed to the official software which is limited to about 1 sample per second.

[Redeeman]

good to hear that it works

Havent tried the official software, in wine or real windows.

I have made my own code (in java though) to handle the bm869s usb data (i have the "official" adapter here).

I plan to write code to handle the bm257s output too, but i dont know when i will get around to it

[cv]

Hi,

I know it is quite some 3 years ago, but anyway:
I also try to build a datalogging cable and have no luck sofar.
My scope (Rigol DS1054Z) does pickup a quite nice waveform, but serial decoding does not give sensible results.
I guess it is the IR diode I am using - an unknown 3 pin IR transistor from a broken device.

But maybe I also do not use the correct settings in my scope for serial decoding.
So: what settings (baudrate etc) did you use in the decode settings?

If I get that right, I may have more luck trying other IR diodes.

[rauldm]

Hi, I did my optical interface with CH340 USB converter, a generic phototransistor, 10k resistor and BC548. I attaching the schemes and software pictures.
I have DM-510A is greenlee version, I got for 60 usd in open box condition. I'm very happy with this meter, I like autochek, is very useful for electric working, you can measure voltage and resistance or continuity without touch your meter.
Regards.