Go Down

Topic: Need help with my first schematic (Read 1 time) previous topic - next topic


Greetings all!  I'm working on a project based on some design advice I got on this forum and I've successfully got the arduino-based project working on my breadboard--I think I'm  ready to move on to the stage of trying to get a PCB made.  I have started working in Eagle and I have made an "attempt" at the schematic.  But, since I am no expert, I wanted to post a screenshot of it and get your thoughts on whether or not I'm good, close, or in real trouble here :)

The basic concept is that this is just a basic PWM LED dimmer controlled via a 10k linear Pot. 5v power comes in via a sparkfun 5v regulated power supply and it connected to a DC barrel jack. I have programmed an attiny85 (which was AWESOME FUN) from my arduino and it basically adjusts the PWM signal going out on PB0 based on the input result it is taking in from the pot on PB3.  The PWM out enters a mosfet setup and goes out through the molex connector (of which only 2 wires will be used).

My LEDs are drawing about .4amps total (about 40 lights) and they are parallel with their own resistors built in.

So, my questions are:
1). Am I missing anything in this schematic that really jumps out at you.  For example "well, if you don't have an X or a Y or a Z right here the entire thing is going to burst into flames"
2) I originally thought the draw from the LEDs was going to be much higher (like 2 amps)--but since it is only .4amps do I even need the mosfet?  I think the arduino can handle up to 1amp can't it (off VIN power)?  But what about the attiny?

Okay, here is a screenshto of where I'm at after my first attempt!


I would put a 10kohm resistor from reset to Vcc, and a 100nF capacitor between Vcc and Gnd


Thanks Emi, is that to stop the thing from just resetting when the power fluctuates a bit?


So like this?


Nov 13, 2012, 05:28 pm Last Edit: Nov 13, 2012, 05:31 pm by Graynomad Reason: 1
but since it is only .4amps do I even need the mosfet? 

You need something, 400mA is about 20x what you should draw from an AVR pin.

Stick with the MosFET, but it has to be a "logic-level" device.

The signal naming on the 4-way connector is a bit confusing.

Rob Gray aka the GRAYnomad www.robgray.com

Go Up