My first project - decade resistor - Page 1
Forum section: electronics / projects

author: Burczyk
author_rank: Contributor
timestamp: February 16, 2018, 06:48:30 am
content: Hello everyone.Im a beginner and i just finished my first project.Its my fourth time trying to post this. It probably wont work this time, too, so im not gonna bother with a detailed description. I really hope its not a lag of some sort so it wont post 4 threads at the same time.I made a 0,8 R - 111 111 100,8 R, 1% Decade resistor. 0,8 R is the resistance of the connectors. Im not looking for alot of accuracy, just somthing that can substitute a 5% E24 resistor value while prototyping on a breadboard.I designed my board in altium designer. I made my PCB at home. I dont know the english name for the technique i used.The project turned out okay.What do you think?EDIT: added photos.While soldering i would put too much solder on the pads and it would flow onto neighbouring pads/traces. Decided im going to tin the short tracks so it looks a bit better.

author: Gyro
author_rank: Super Contributor
timestamp: February 16, 2018, 09:05:31 am
content: Welcome to the forum.Nicely done, and very cost-effective.

author: Vic20
author_rank: Contributor
timestamp: February 17, 2018, 01:30:35 pm
content: Nice work.Don't know if adding solder "looks better" but it sure decreases track resistance. This use of solder is quite commonly used in power supplies.I understand that track resistance is not a problem in your case or you would have used thicker tracks on the long lines. Off course you can also add solder to them.The kind on jumper connectors you are using are not designed to provide a short resitance path as you have already seen. Probably a DIP switch would be better as they can have 20 mOhm contact resistance or less and they are better sealed for environmental degradation. Something like:http://www.farnell.com/datasheets/1792293.pdf?_ga=2.214187735.1115380899.1518860233-2110827601.1509204109Or a rotatory like that: (although it has worse resistance)http://www.farnell.com/datasheets/1783607.pdf?_ga=2.243357381.1115380899.1518860233-2110827601.1509204109But it depends on your needs.I understand that using 1% resistors will limit the number of usable digits to 2 or 3. But I think that it is fine.

author: Burczyk
author_rank: Contributor
timestamp: February 18, 2018, 06:07:05 am
content: I have thought about changing my headers and jumpers to gold-plated ones. Would it reduce the contact resistance significantly?

author: Gyro
author_rank: Super Contributor
timestamp: February 18, 2018, 10:31:15 am
content: Very doubtful - Gold isn't used for its conductivity, just lack of oxidation. The wiping action of your jumpers is enough to ensure good contact. I wouldn't risk messing up the PCB by changing them.Solder doesn't actually reduce track resistance much either (like Gold, it isn't a particularly good conductor compared to Copper and Silver), what it does do is prevent your bare copper tracks from oxidizing and improve their thermal mass / heat dissipation area. It's worth tinning the tracks on something you're handling a lot to prevent acids from your fingerprints from staining the tracks.