BM235 Modification Questions - Page 1
Forum section: electronics / testgear

author: Tones
author_rank: Unknown
timestamp: May 23, 2018, 02:28:08 am
content: Hi All,I will post 2 questions first and then qualify in the next post.- The teardowns mostly show unsoldering the input board to investigate further. Can those orangey-red leads be replaced by headers like those already fitted?- The solder pads associated with the fuse holders look untidy. Can I reflow some nice new solder to make them more "robust"?

author: Tones
author_rank: Unknown
timestamp: May 23, 2018, 02:58:21 am
content: Hi Again,I posted this initially, but it was very wordy, and the pics were too big so I have resized them.I have read & re-read most of the words & pics associated with this device. I would not normally take something new apart "If it ain't broke .... ", but with Dave's admonition "Don't turn it on, take it apart!".I have used someone else's pics. Hopefully, I haven't broken any rules or made someone upset (https://lygte-info.dk/review/DMMBrymen%20BM235%20UK.html)I am waiting on my shite-and-briney new meter from Dave.I am a tinkerer (thank you Massimo Banzi).There looks to be plenty of real-estate to accommodate headers, except the longer lead is offset. I class myself as quite capable of physically accomplishing the tasks, but inexperienced as far as technical understanding.To my way of thinking the soldering on the main pads looks "unfinished". They are probably quite ok. I guess economically that amount of solder over many many units adds up. I learnt many moons ago the biggest failure rate on anything electronic, are the solder joints, not components.Anyway, I look forward to your comments.CheersTony

author: JS
author_rank: Frequent Contributor
timestamp: June 01, 2018, 09:03:54 am
content: The solders looks ok, what are you trying to accomplish?For mods, if you are bored, I was looking to add the IR serial connection, as I recall dave found that the pads where the IR LED should be was going was the LCD display bus, which is quite consistent given the BM250 and BM250 series protocol is the LCD protocol, both available in the site, BM250 uses 15 bytes at (9600, N, 8, 1) com while BM200 uses 13 bytes (2400, N, 8, 1) plus a reserved byte at the end. First nibble is byte number, second data (each bit corresponding to a bit on). 7 segments should be decoded to BCD and then probably translated to hex.I see two caveats, first the BM250 needs to start with the hold button pressed to start serial com (why if it's same LCD data line?) while BM235 shows the firmware version with that operation.And second, the LCD from the BM235 is not exactly like the BM250 series, so segments might not be in the same position, but this is readjusting the table with some experimentation.I don't see me putting to work on this right now as I have a ton of things to make in my lab and a 121GW on the way for the tasks the serial com would be useful, but I don't see it too hard to do if someone start to play with, I haven't seen anyone yet. It could be as straight forward as soldering the LED and using the BM250 soft to record the data, at least if numbers segments fall in the same places you can throw away the units as you know what you are measuring, I guess you won't miss by 3 orders of magnitude very often due to auto-ranging. If it's not just like that it might be a tad harder as a code should be developed from the ground up to decode the data... Some probing to the data line should tell the truth.JS