My First project finished. With video.  - Page 1
Forum section: electronics / beginners

author: Dellyjoe
author_rank: Regular Contributor
timestamp: June 27, 2013, 07:57:00 pm
content: hello everyone this is my first project.There is the schematicEnd here are the two videos, the switches on the right i need to fix i just kind of put them on really fast, so do not look at them.Here is the music box in actionAnd here is what it looks likeumm like i said this was my first project something small but fun, and something that would take me more then a couple of days to make.

author: kizzap
author_rank: Unknown
timestamp: June 28, 2013, 12:13:48 am
content: Is it just me, or should resistors R15-R18 and R32-R35 be connected between the base of the transistor and the op amp, with increasing values of resistance along the lot?Current limiting is already handled by the resistor between the LEDs.-kizzap

author: poorchava
author_rank: Super Contributor
timestamp: June 28, 2013, 06:18:53 am
content: I think he just wanted 8 leds total per channel, but considering the Vce drop you can't run more than 2 in series from 6V power supply.

author: dr_p
author_rank: Frequent Contributor
timestamp: June 28, 2013, 06:43:32 am
content: Yes, but there are no base resistors on those transistors.And there are extra resistors from the emitters to ground. I think these might limit the base current, since it's actually IBE,so the base current flows out of the emitter, but that will also affect the collector current going to the LED. I've never seen this approach before though. Maybe because it's wasteful.

author: ttp
author_rank: Regular Contributor
timestamp: June 28, 2013, 12:35:37 pm
content: Quote from: dr_p on June 28, 2013, 06:43:32 amIt makes sort of voltage controlled current source - LED current is proportional to base voltage.ILED=(VB-VBE)/REwhere VBEis about 0.65V depending on transistor used

author: cthree
author_rank: Frequent Contributor
timestamp: June 28, 2013, 08:12:13 pm
content: Congrats on your first project!! Add your country to your profile so we know where you areLooks like it was a lot of fun and must have been very rewarding to see it work for the first time!Some good advice above. You might consider moving your LED current limiting resistors R15-18 and R32-35 to the other side of your transistors and you should add resistors to the base of the transistors.As an alternative design did you consider driving the LEDs in parallel using just a single low-side BJT per colour? You've got a lot of transistors in parallel there doing pretty much the same thing. It appears the LEDs just glow together and that you aren't looking for any sort of meter effect. Would lower your part count and simplify. I'm not sure if I didn't miss some subtlety of the design. Perhaps for Rev B?

author: Dellyjoe
author_rank: Regular Contributor
timestamp: June 28, 2013, 09:24:11 pm
content: Quote from: cthree on June 28, 2013, 08:12:13 pmThank you cthree ,i did have a great time making this project and cant wait to find a new one to start, i will add my country right now so everyone knows were im from.i will look into simplifying my project.thanks for everyone posting in this topic thanks for helping me out.