5 transistor esr meter - Page 1
Forum section: electronics / beginners

author: spdf
author_rank: Contributor
timestamp: July 11, 2017, 03:20:36 pm
content: Hello guys,recently I build 5 transistors esr meter and I found out that on short condition my ammeter value keeps dropping down. After like 5 shorted measurements it shows only half scale ~25 uA. I tried to change R24 with lower value from 300 to 100r (my ammeter is 1900r) but with no luck on general condition.Any thoughts where I should look? Any help would be appreciated!

author: hugo
author_rank: Regular Contributor
timestamp: July 12, 2017, 10:46:38 pm
content: Hi,Have you seen these:https://youtu.be/3fiUZZlveS0https://www.eevblog.com/forum/projects/5-transistor-esr-meter-design/100https://www.eevblog.com/forum/projects/jay-diddy-5-transistor-esr-meter/msg933224/#msg933224Have you checked the DC voltages ?

author: spdf
author_rank: Contributor
timestamp: July 13, 2017, 07:17:44 pm
content: Ok I measured DC voltages and I have different values on Q5 on collector 1.99V and on base 1.58VI am powering it up from 12V is that make any difference?

author: hugo
author_rank: Regular Contributor
timestamp: July 14, 2017, 12:21:08 am
content: "Ok I measured DC voltages and I have different values on Q5 on collector 1.99V and on base 1.58V" ...That's your problem, check the values of R18, R19, R21, R22, Q5, what kind of diodes, uammeter do you have, R23 (10k) ?"I am powering it up from 12V is that make any difference? " ... nope .

author: spdf
author_rank: Contributor
timestamp: July 14, 2017, 06:26:01 am
content: I double checked everything and I found these differences from original schemeR12 33rR10 3.3rdiodes are D3/D4 1n5711 and D1/D2 1N4002, uammeter is 50uA and 1900 ohm R23 is 10k potentiometer.Still don't have a clue what is wrongAnd just for the record this is my first project that I have ever made so it's highly possible that I am missing something obvious ;]

author: amspire
author_rank: Super Contributor
timestamp: July 14, 2017, 12:26:04 pm
content: Quote from: spdf on July 14, 2017, 06:26:01 amThe clue is in Hugo's post:Quote from: hugo on July 14, 2017, 12:21:08 am1.58V on the base is not possible unless something is wrong in the circuit. The R21/R22 voltage divider can only have a maximum voltage of 5V x 10/37 = 1.35V. Base current can lower this, but cannot increase it. It cannot be 1.58V.So the most like fault is that one or both of R21 or R22 are wrong. For example, R21 is 22K instead of 27K. If that is not the problem, there is something else wrong in that part of the circuit. Faulty connections, strange Q5 problem, something in that Q5 circuit.Richard

author: hugo
author_rank: Regular Contributor
timestamp: July 15, 2017, 12:27:45 am
content: Could you post a picture of your board, high resolution if possible ?Amspire is right "For example, R21 is 22K instead of 27K."

author: spdf
author_rank: Contributor
timestamp: July 18, 2017, 09:48:22 am
content: After a lot of soldering and desoldering I've got damaged my pcb, so a made a new one and everything worked like a charm from the first attempt.It seems there was a problem with a contacts after all.I would like to thank you guys for your help! Really appreciate that!

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 18, 2017, 07:55:38 pm
content: Quote from: spdf on July 18, 2017, 09:48:22 amHi spdf,I am glad to hear that it works. Would you like to post a picture of your board and meter in the main thread?https://www.eevblog.com/forum/projects/5-transistor-esr-meter-design/msg171364/#msg171364Jay_Diddy_B