Go Down

Topic: No Serial communication (not 10k resistor problem) (Read 1 time) previous topic - next topic

sti robot

Jun 11, 2007, 06:54 pm Last Edit: Jun 11, 2007, 06:58 pm by sti_robot Reason: 1
According to the manufacturer the ATMega168 operates up to 185F (85C).  I can see it reaching that temperature range where I mounted it.  I mounted the arduino in the dash on top of the ducting for the AC.  The AC was not on at the time (windows down for safety, etc. at driving even).

If this is the case.  What exactly happens when the temperature gets that high?  Bit start flipping?  

As far as a solution I'm thinking of hooking up some temp sensors (I'll be developing for them anyway) to that area.  I could mount it in another location (easy), I could add a heat sink to the chip and a fan (also relatively easy).


sti robot

I think I may have figured it out!!

Being that I'm a software guy I never am really concerned for these EE type issues.  I got in all my sensors and was thinking of hooking them up when I started to think about the power they draw.  

I believe I may be drawing too much power out of the 5V power onboard the arduino causing it to loose memory/crash. (see: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1178565105/4#4)

Apparently it has a ~400mA current limit (http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1183268436/2#2)

In the current setup I am powering a serial LCD (I believe it draws ~60mA with the backlight and an accelerometer which should be using only 0.6 mA).  So I'm not sure how this is the problem.  It could also be a noisy power supply from the car.  Cars have a problem delivering a nice even 12V.  Sometimes its 13something and sometimes under load it can be lower.

All the sensors I'd like to power off the 5V:

1 accelerometer drawing 0.6mA
2 buttons drawing 2mA each (using 2.2kOhm resistors...set to HIGH normally open)
2 thermistors in voltage dividers using 2.5kohm resistors providing 790-18680Ohm's themselves ???draw each??
1 pressure sensor drawing 0.5mA

This should all work correctly right (we're way far from 500mA)?
What about the voltage dividers?? How much do they draw/how do i calculate that?

sti robot

There are a couple of things to keep in mind when developing electronics for an automotive environment.

The power supply and long signal lines are subject to a great deal of electrical noise--which can cause intermittent hard to diagnose problems.

Second there is a great deal of vibration which requires that all devices have a solid mechanical as well as electrical connections.

If your project works well on the bench but problems appear in the car then one (or both) of these two areas are the likely source of the problem.

If there are power supply problems from the 12V coming from the car how do I fix them?


Make an additional power supply that takes the automobile power and cleans it up.


That's a pretty good circuit, you can leave out the relay and it's control circuitry unless you have a need for it. As well as some of the other connectors and wires.


I really like the specifications of that part but you can use about any three terminal regulator fixed or adjustable that's within the Aruduino's recommended voltage and current rating. Just setup an adjustable one properly and you're set.

If it was designed by man it can be repaired by man.

sti robot

^ I'm beginning to agree with your theory.  Power output from a car's 12V system really isn't 12V but something the range of 12V to 13.5V normally.

Should a sustained 13.5V cause the issue I am seeing (flipped bits on the chip)?  I am driving the car hard so the power steering pump, iginition, and other engine related electrics are getting a workout.  

Go Up