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| Brymen BM86x Backlight Duration Mod |
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| SMB784:
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-0197-0000 The 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 rumored to be a clone or close cousin of the FS970X The 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 an EEPROM (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. |
| Corner:
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. |
| SMB784:
So it has been claimed that the EEPROM stores the calibration data for 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. |
| CDaniel:
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 |
| SMB784:
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. |
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