Go Down

Topic: Police light set up in car and power. (Read 3 times) previous topic - next topic

CrossRoads

Sharing current - is that really more of a concern where LEDs with different characteristics are used?  I have 8 digits with 7 segments each made of 3 parallel LEDs & decimal points made of 2 parallel LEDs being driven by a MAX7221, multiplexing at 800 Hz (not user changeable). Some digits use Red LEDs, some digits use yellow LEDs, some digits use Orange LEDs. I have been testing with this setup for a while, letting it run for hours at a time, and I am not seeing any visual difference in intensity anywhere.
I also have some really bright (10,000)mCD capable white LEDs paired up in parallel, driven by a 7406, that are not turned on anyhwere nearly as often as the digits, that seem to be doing okay.

I'll have to break open a couple of lines and stick a really low value resister in, measure the voltage across it on a scope and see what current they're actually running at.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

Roman G

Thanks guys for the replies

CrossRoads,

i made a diagram of what i understand it to be. However i tried searching for the IRF3707Z or 7406 ic but to no avail. Please point me in the right direction. is it also availbale from pololu? so i can order everything at once? I tried radioshack and the like and none have IRF3707Z.



I want this done before new years so i will overnight parts however i dont know what to order.

red leds are rated at 20mA and 2.0v
blue leds are at 20mA and 3.3v or so.

which resistors do i need?

I used online calculator and for the blue i got 390 ohm resistor if wired by 4 in series with 8 rows

and for red i got 220ohm if using like u suggested

Thanks for any tips i really appreciate it

Roman

Big Oil

For my Christmas decoration I did 22 LEDs all in parallel, straight off a pin, with a second set on another pin.
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1291875201/0#0

CrossRoads

Ok Roman, that is a shame, I bought 10 of those a while ago & now can't find them anywhere.

I searched at mouser.com, and found this part that will do nicely instead.
http://se.mouser.com/ProductDetail/NXP-Semiconductors/PSMN035-150P127/?qs=sGAEpiMZZMvKM5ialpXrmoKPBF94BAPg

Your schematic is not quite correct.
Make sure to connect up like I have shown - 20V is the top of LEDs in series, finish with the resister going to the Drain pin of the MOSFET, with the Source pin to ground. With this  MOSFET you are opening & closing the circuit on the Ground side, and not on the high voltage side.

Connect the Arduino pin to the gate thru a 1K resistor, with a 10K to ground.

Mouser also has 7406's in stock
http://se.mouser.com/ProductDetail/Texas-Instruments/SN7406N/?qs=sGAEpiMZZMtYFXwiBRPs0wQlaYsWIJgx

Your resister choices look okay.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

Roman G

Hi CrossRoads,

sorry to bother again but i am stomped.

I have received all the parts and i am lost as to how to properly connect everything.

I ordered 2 mosfets transistors, 3 7406s and not sure which is better to use and finally got the voltage booster.

Please help me with a sketch. I dont understand how do i connect the second part of leds (blue ones, according to the sketch) if it only has 3 pins.

Please help i would love to finish this by the end of the week if possible.

any suggestions are appreciated

Thanks a bunch

Roman

Here is the current one i just cant understand how to finish it.


Go Up