[Help] How to switch BM235 OUT of hexadecimal display mode.  - Page 1
Forum section: electronics / testgear

author: ArsenioDev
author_rank: Frequent Contributor
timestamp: April 04, 2022, 09:04:26 pm
content: Hey, figured I should ask here of all places.About a month ago my BM235 decided to switch into hexadecimal display mode and I'd REALLY like it switched out. Attached is an image of it testing a 10K resistor, it does this hex display in all modes EXCEPT AUTOV.Cheers

author: EEVblog
author_rank: Unknown
timestamp: April 06, 2022, 11:36:44 pm
content: I'd say remove the LCD and give the zebra strip and contacts a good clean.

author: Brumby
author_rank: Unknown
timestamp: April 07, 2022, 02:07:16 am
content: Yeah, I agree.Interesting that you have, what I believe is, an 8.00kΩ resistance with what is purported to be a 10kΩ 5% resistor. 20% low is a bit hard to believe even for the cheapest Chinesium stuff I've ever encountered. I'm also intrigued by the fact that we can't see whether those probes are what is plugged into the meter or whether there is anything else connected.Call me suspicious ....

author: Fungus
author_rank: Super Contributor
timestamp: April 07, 2022, 07:00:34 am
content: Quote from: Brumby on April 07, 2022, 02:07:16 am"A" is ten in hexadecimal, hence "hexadecimal display".It's not a missing segment, it's showing the value in hexadecimal.

author: ArsenioDev
author_rank: Frequent Contributor
timestamp: April 07, 2022, 02:56:00 pm
content: I'll clean the contacts later today.It's DEFINITELY tracking as expected on hex, goes 0-9 then A-F as expected.

author: ArsenioDev
author_rank: Frequent Contributor
timestamp: April 07, 2022, 03:18:29 pm
content: Update: tore it down, full clean of the zebra, contacts and wiper for selector while I was at it. No dice, still Hex.Pic related of testing a 12V5 rail on my power supply, hex is correct.The only autorange that works is this AutoV/LoZ

author: bdunham7
author_rank: Super Contributor
timestamp: April 07, 2022, 03:34:08 pm
content: What happens at 17.xx volts? As you go up and down in voltage, is it the characters to the left of the decimal that are hex or something else?

author: ArsenioDev
author_rank: Frequent Contributor
timestamp: April 07, 2022, 04:01:52 pm
content: It says "11.xx" where decimals are non-hex.

author: TimFox
author_rank: Super Contributor
timestamp: April 07, 2022, 04:04:13 pm
content: Quote from: Fungus on April 07, 2022, 07:00:34 amA humor book about data processing had mnemonics for the six extra hexadecimal digits, based on demonic names: Asmodeus, Beelzebub, etc.https://openlibrary.org/books/OL4255689M/The_devil%27s_DP_dictionary

author: ejeffrey
author_rank: Super Contributor
timestamp: April 07, 2022, 04:25:37 pm
content: No idea how to fix it, but that is a pretty cool failure mode.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 07, 2022, 04:47:42 pm
content: Ooh, undocumented?It's not quite correct, or complete, anyway? 0.51 (dec) falls between 0.82-0.83 (hex).Is there something about the controller / display driver that has a hex mode somehow? Say by pulling a pin somewhere (or not, say a trace broke instead)?Tim

author: bdunham7
author_rank: Super Contributor
timestamp: April 07, 2022, 05:19:24 pm
content: Quote from: ArsenioDev on April 07, 2022, 04:01:52 pmAnd if you switch it to AUTO V/LO-Z without changing anything else, then it reads "17.xx" volts?I'm doubtful that would be an intentional hidden mode that could be switched on and off, there's likely some other error internal to the chipset. Interestingly, the BM235 uses a separate HY2613C LCD driver, so you theoretically have access to the interface between the two chips.Dave did a pretty good video here:https://www.eevblog.com/forum/blog/eevblog-912-bm235-multimeter-reverse-engineering/

author: AVGresponding
author_rank: Super Contributor
timestamp: April 07, 2022, 05:21:08 pm
content: Quote from: T3sl4co1l on April 07, 2022, 04:47:42 pmPretty sure 0C16=1210. Maybe you misread? From what I can see, it's one count out, reading 0C.51VDC for a supply of 12.50VDC. I'm certain that is within the combined uncertainty of meter and PSU.

author: bdunham7
author_rank: Super Contributor
timestamp: April 07, 2022, 05:33:13 pm
content: Quote from: T3sl4co1l on April 07, 2022, 04:47:42 pmI think is probably the result of using a BCD output to a display section that is HEX capable. A failure of that digit's BCD counter to reset and increment results in an illegal HEX output. This may be right in the ADC section itself--I know of earlier dual-slope ADC designs that used a chain of BCD counters directly, followed by a set of latches and then the actual display output circuitry and not much else. I don't know the method of interface between the HY2613C and the BTC ASIC, but I suppose it's there in the datasheet.Edit: I read a bit more and the interface is I2C.

author: ArsenioDev
author_rank: Frequent Contributor
timestamp: April 07, 2022, 05:41:35 pm
content: Quote from: bdunham7 on April 07, 2022, 05:19:24 pmBang on, that's precisely what it does. Only the leading digits in regular modes go hex, decimals are normal binary.

author: TheSteve
author_rank: Unknown
timestamp: April 07, 2022, 06:06:22 pm
content: So really you have a very exclusive hex edition of the BM235 - maybe try to sell it for double.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 07, 2022, 06:43:23 pm
content: Quote from: AVGresponding on April 07, 2022, 05:21:08 pmNah I mean if the whole thing were completely, and correctly, hex formatted. In 16.16 binary fixed point, that reading would be represented 0x0c82 or 0x0c83. Or as we usually write numbers, "C.82" (vs "12.51"). That is, every position past the decimal point is 16^-1, 16^-2, etc. times the numeral value, just as digits to the left are 16^0, 16^1, etc. So, it's interesting that it only seems to do it, either to the ones-column, or integral digits (left of the point).What does it do at other values, like uh, got anything that can do >160V?Also does it affect current? Capacitance? Frequency? Resistance is shown, though I'd be curious if it's relative to range or position (try other decades of values?).I suppose diode isn't affected, but that's a small reading, and if it's only reading out the integral digits in this way, it wouldn't actually show anything different.Tim

author: ArsenioDev
author_rank: Frequent Contributor
timestamp: April 07, 2022, 07:21:02 pm
content: Quote from: T3sl4co1l on April 07, 2022, 06:43:23 pmANY autorange mode reads out the leading digits as hex, manual range switching does make it show the correct number in binary. It's downright bewildering.

author: EEVblog
author_rank: Unknown
timestamp: April 08, 2022, 10:14:24 am
content: I've asked Brymen.