Brymen BM86x Backlight Duration Mod - Page 1
Forum section: electronics / testgear

author: SMB784
author_rank: Frequent Contributor
timestamp: July 21, 2020, 03:36:07 pm
content: Hey everyone!Like many of you, I love my Brymen BM867 multimeter. Its a great meter for the money with loads of functionality, and even a nice, bright backlight. However, for my purposes the backlight doesn't stay on long enough - a mere 15 seconds! - and there doesn't appear to be a way to adjust the duration from within the existing software. As such, I would like to look in to how to adjust the firmware running on this device so that the back light duration can be modified to be of indefinite duration. The current backlight can be toggled on and off by holding the select button, and times out after 15 seconds if it is not switched off manually. Ideally the mod would increase this timeout to a very long time (a minute or more), possibly up to the auto-shutoff time for the meter itself.As a caveat, I recognize that the 15 second duration is designed to limit battery usage and extend battery life, however I am not really concerned with that, and I am more than happy to replace batteries frequently.The two chips that seem to run the thing are labelled BTC-85-4 and BTC-0197-0000The first one is the ADC chip, which might also contain a microcontroller but more than likely seems to just sort out signal processing.It is rumoredto be a clone or close cousin of theFS970XThe second one is likely the display driver, and it may also serve as the master microcontroller that governs the operation of the device. It has anEEPROM (a 4kB S24CS0A4)associated with it which may contain the firmware (located at U5)Any advice on how to go about this? Maybe reading the EEPROM is a good start.

author: Corner
author_rank: Regular Contributor
timestamp: July 22, 2020, 07:27:45 am
content: I too I'm bothered by the short backlight duration. The backlight on the F87V is great to use in contrast. I'd like to mod it but I don't have the knowledge to do so.

author: SMB784
author_rank: Frequent Contributor
timestamp: July 22, 2020, 12:52:49 pm
content: So it has been claimed that the EEPROMstores the calibration datafor the meter; it is unclear whether or not it also stores the firmware. There is a tx/rx pair of pins going to the display, perhaps the main chip communicates with the display via SPI or UART, which can be tapped to see if there is useful information being transmitted.

author: CDaniel
author_rank: Frequent Contributor
timestamp: July 22, 2020, 02:50:31 pm
content: Coud be much easier to add a small microcontroller to control directly the backlight from the backlight button, of course if the leds wires are accessible

author: SMB784
author_rank: Frequent Contributor
timestamp: July 22, 2020, 06:51:39 pm
content: After doing some sleuthing, it would appear the large chip (BTC-0197) might just be an LCD display driver with no associated microcontroller capabilities. That leaves the AD-85 chip to be the brains behind the operation; if it is truly an FS970X it should have an onboard microcontroller that could execute firmware. One possibility I will explore is to trace the LED backlight signal to a chip and see where it ends up - at the AD-85 or the BTC-0197.

author: chemik22
author_rank: Newbie
timestamp: March 04, 2024, 06:11:44 pm
content: Quote from: SMB784 on July 22, 2020, 06:51:39 pmHave you found anything useful to solve the backlight timer problem ?

author: coromonadalix
author_rank: Super Contributor
timestamp: March 04, 2024, 06:25:40 pm
content: for some fluke you had a capacitor change who helped getting the power down delay longer, for backlight ?? you have to find the datasheet of the ic's ... if they existthe BTC chip seems custom, send an email to Brymen and or Grenleesince there is no schematics floating around ?

author: IanB
author_rank: Super Contributor
timestamp: March 04, 2024, 06:41:47 pm
content: To the best of my understanding, the backlight timer is programmed in the firmware. It can only be modified with new firmware, and that is not an aftermarket option. The only option would be to buy a new meter from current production.

author: chemik22
author_rank: Newbie
timestamp: March 05, 2024, 10:55:23 am
content: Ech.. I have just had a hope that it can be finally solved by simple hard soldering and turn the light constantly without capability to off it. But probably if nobody did that think before I guess it is not possible.

author: shakalnokturn
author_rank: Super Contributor
timestamp: March 05, 2024, 11:14:58 am
content: First do a little reverse engineering see if it's an external RC monostable triggered by one of the "BTC's"? (Doubtful...)Next some bus sniffing, if you're lucky and it is EEPROM set, it may fetch the constant each time backlight is enabled, in that case once you have the address it's a matter of playing with the data value. Easy enough.If IanB is right chances of existing software modification are low. In this case I'd go for kludging-in a monostable of one sort or another. The PIC 10F MCU's in SOT-23-6 would be my choice for this kind of job. If you can tap in to the keypad easily it even allows you to set different modes depending on key usage. (ie: Long press->enable BL for 15 min, Longer press-> enable until DMM power off. It would also leave the option to disable BL manually without power cycle if needed.)As for having the BL constantly on... If you really need it that much... I'd at least try to tie it to the auto power off timeout so you don't drain the battery if you leave for coffee and never return to work.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 05, 2024, 01:09:20 pm
content: Quote from: IanB on March 04, 2024, 06:41:47 pmhttps://youtu.be/bDIx4ik0vvA?t=698

author: Fungus
author_rank: Super Contributor
timestamp: March 05, 2024, 01:46:03 pm
content: Add a flip-flip to the LED circuit so that pushing the backlight button toggles it on/off.

author: mwb1100
author_rank: Frequent Contributor
timestamp: March 05, 2024, 10:01:24 pm
content: Has anyone dumped the EEPROM from any of the BM86x family (including the BM525/BM521)? I suspect there's a half decent chance that there's a byte in the EEPROM for the number of seconds the backlight stays on.

author: IanB
author_rank: Super Contributor
timestamp: March 05, 2024, 10:48:56 pm
content: I don't think anyone knows for sure that there is an EEPROM in the meter. Based on interactions between user joeqsmith and Brymen, it might be that the firmware is stored in non-erasable ROM and the only way to change it is by chip replacement.

author: shakalnokturn
author_rank: Super Contributor
timestamp: March 05, 2024, 11:43:36 pm
content: There's a difference between firmware in mask ROM or flash in the MCU and configuration data that may be also stored in the MCU (though not in mask or OTP ROM) or in an external EEPROM.If you ask me the BM867 has a 24Cxx on the top PCB...https://www.eevblog.com/forum/testgear/brymen-bm-867-teardown-pictures/?action=dlattach;attach=31973;imageBM869:https://www.flickr.com/photos/eevblog/8513690107/in/album-72157632878242654/BM525 has a lot of EEPROM must be mainly for the logging.https://lygte-info.dk/pic/Brymen/BM525s/DSC_8868a.jpgI have a dump from a Greenlee BM251 if that's of interest.

author: mwb1100
author_rank: Frequent Contributor
timestamp: March 06, 2024, 07:48:29 am
content: Quote from: shakalnokturn on March 05, 2024, 11:43:36 pmIf I'm not mistaken, that's a Greenlee DM-100A == BM251 with a backlight (approx 30 seconds)?If someone were willing to monkey around with a DM-100A EEPROM (surely there's calibration data in there, so some risk of really screwing up your meter): I'd look for something like 0x20 in the EEPROM (32 seconds) and see if changing that to a significantly smaller or larger value makes a corresponding change to the backlight duration. Of course even if that works it only hints to the possibility of a BM867 doing something similar, and almost certainly not in the same EEPROM location.I have a BM257, but don't have access to an EEPROM reader/writer.

author: coromonadalix
author_rank: Super Contributor
timestamp: March 06, 2024, 09:26:12 am
content: in the brymen eevblog model, i think DAVE stated at one time, it needed a programmer to access some ..... he would not go that far in explanationsFor the higher modelsduno ??

author: shapirus
author_rank: Super Contributor
timestamp: March 06, 2024, 09:39:21 am
content: Quote from: IanB on March 05, 2024, 10:48:56 pmThere should be. The meter has to store its calibration data somewhere, and there is a procedure to recalibrate them, so it's not read-only.edit: ...but of course the delay time may be hardcoded in the firmware itself, which may be stored in a ROM, which apparently is the case.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 06, 2024, 01:42:16 pm
content: Quote from: mwb1100 on March 05, 2024, 10:01:24 pmQuote from: IanB on March 05, 2024, 10:48:56 pmThe following was from my discussions with Brymen about increasing the BM869s's backlight timeout.Me:QuoteBrymen:QuoteMe:Quote

author: shakalnokturn
author_rank: Super Contributor
timestamp: March 06, 2024, 05:11:50 pm
content: Quote from: mwb1100 on March 06, 2024, 07:48:29 amIt's a DM-200A, backlight is about 30s.I have a second one around that I'll dump when I clean the switch. It will at least show the memory locations that have identical values on 2 different meters.Quote from: joeqsmith on March 06, 2024, 01:42:16 pmThat only makes half sense to me:Calibration constants can't be in OTP MCU (at the best they could store coarse default values) and various photos show EEPROMs, replacing the MCU is not replacing the ADC so their comment is true only if the new firmware uses different EEPROM addresses for calibration.

author: IanB
author_rank: Super Contributor
timestamp: March 06, 2024, 06:02:43 pm
content: Quote from: joeqsmith on March 06, 2024, 01:42:16 pmQuote from: shakalnokturn on March 06, 2024, 05:11:50 pmIf you disassemble the meter, unsolder a chip, and solder in a new chip, that is major surgery on the meter. If you want to trust the meter after such work, it would clearly be sensible to do a re-calibration and retest. It's a recommendation, not a requirement.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 06, 2024, 07:35:22 pm
content: Quote from: IanB on March 06, 2024, 06:02:43 pmAgree. During that video, after swapping the part, I run through the same basic checks and didn't notice it having any effect on the measurements.***QuoteThat video is 3 years old. I am a bit surprised that someone with a older meter would necropost about it today.***Quote from: shakalnokturn on March 06, 2024, 05:11:50 pmCalibration constants have nothing to do with the backlight timer, which is hard coded in the firmware. Calibration does not suggest realignment. As IanB mentions, calibration was only recommended to make sure the meter was still functioning.Quote from: Fungus on March 05, 2024, 01:46:03 pmI like my auto dimming backlight on my UT61E.https://youtu.be/S36LfKmSjKw?t=332