LED test help

[accole]

I am a novice in electronics so small word replies please

I am (to prove I can) trying to make 8 LEDs turn on/off in sequence (similar to the ones on the front of KITT for those who remember Knight Rider). I have a 28x1 project board (so with the octal darlington on it).

The simulator software suggests I have my program right, but when I connect it all up the LEDs do not light up, and the battery pack gets very hot! Short circuit somewhere??

I have a V+ feed from the output pins by the darlington going to my breadboard, and that is the +ve for the LEDs. The -ve side of LEDs goes to the output pins (as I know the darlington is a power sink (or whatever it should be called).

Any ideas what I am doing wrong?

 

[kevrus]

Welcome to the forum, a picture or diagram would help faultfinding, do you have current limiting resistors connected in series with the LEDs?

 

[Andrew Cowan]

That means you're shorting the battery.

Is there a solder blob connecting +V and 0V? If not, does anything else get hot? That would help us find out where the short circuit is.

A

 

[hippy]

Are you using current limiting resistors with your LED's ?

You cannot connect the LED's directly between +V and the darlington outputs. Too much current will flow which causes overheating and potentially damages components. A suitable value of resistor is usually between 330R and 1K. The lower the value the brighter the LED will be.

If you disconnect the LED's and it still gets hot then there is something else wrong with the circuit construction, probably as hort as Andrew suggested.

 

[accole]

Update

Thanks everyone. It was a dodgy ribbon cable (out of a PC!) I was using to link the project board with my breadboard .. having replaced it with a new one it now works ok

 

[Haku]

I am (to prove I can) trying to make 8 LEDs turn on/off in sequence (similar to the ones on the front of KITT for those who remember Knight Rider). I have a 28x1 project board (so with the octal darlington on it).

That's yet another one of the reasons I got into programming Picaxe chips, the Hitari R/C KITT looks brilliant but it drives like complete crud and the front scanning light only has 5 LEDs!

I won bidding on a 2nd yesterday, boxed but doesn't drive, so I'm going to replace the radio gear with 'proper' proportional stuff so the car can drive as good as it looks, and also replace the pathetic scanning light with the proper number of 8 LEDs driven by a Picaxe 18X.

In testing I tried putting some high value capacitors on the LEDs so they would fade out after the voltage to them was stopped, but the fading didn't work very well. It wasn't until I saw the threads doing software PWM to drive RGB LEDs that I got the tip to use PulsOut, resulting in this program I quickly whipped up:

#picaxe 18x

'KITT scanning light

symbol pawz=24
symbol z1=255
symbol z2=100
symbol z3=33
symbol z4=7
symbol z5=1
setfreq m8


do
 for b0=0 to pawz:pulsout 0,z1:pulsout 1,z2:pulsout 2,z3:pulsout 3,z4:pulsout 4,z5:next b0
 for b0=0 to pawz:pulsout 1,z1:pulsout 0,z2:pulsout 1,z3:pulsout 2,z4:pulsout 3,z5:next b0
 for b0=0 to pawz:pulsout 2,z1:pulsout 1,z2:pulsout 0,z3:pulsout 1,z4:pulsout 2,z5:next b0
 for b0=0 to pawz:pulsout 3,z1:pulsout 2,z2:pulsout 1,z3:pulsout 0,z4:pulsout 1,z5:next b0
 for b0=0 to pawz:pulsout 4,z1:pulsout 3,z2:pulsout 2,z3:pulsout 1,z4:pulsout 0,z5:next b0
 for b0=0 to pawz:pulsout 5,z1:pulsout 4,z2:pulsout 3,z3:pulsout 2,z4:pulsout 1,z5:next b0
 for b0=0 to pawz:pulsout 6,z1:pulsout 5,z2:pulsout 4,z3:pulsout 3,z4:pulsout 2,z5:next b0
 for b0=0 to pawz:pulsout 7,z1:pulsout 6,z2:pulsout 5,z3:pulsout 4,z4:pulsout 3,z5:next b0
 for b0=0 to pawz:pulsout 6,z1:pulsout 7,z2:pulsout 6,z3:pulsout 5,z4:pulsout 4,z5:next b0
 for b0=0 to pawz:pulsout 5,z1:pulsout 6,z2:pulsout 7,z3:pulsout 6,z4:pulsout 5,z5:next b0
 for b0=0 to pawz:pulsout 4,z1:pulsout 5,z2:pulsout 6,z3:pulsout 7,z4:pulsout 6,z5:next b0
 for b0=0 to pawz:pulsout 3,z1:pulsout 4,z2:pulsout 5,z3:pulsout 6,z4:pulsout 7,z5:next b0
 for b0=0 to pawz:pulsout 2,z1:pulsout 3,z2:pulsout 4,z3:pulsout 5,z4:pulsout 6,z5:next b0
 for b0=0 to pawz:pulsout 1,z1:pulsout 2,z2:pulsout 3,z3:pulsout 4,z4:pulsout 5,z5:next b0
loop