I have built a 7 LED chaser circuit running on 18V. I changed one LED for a copper coil to run an electromagnet but it didnt have enough power, then i added a darlington pair I had from the early 90's never used before the same output and it worked for a bit i added a switch so it could be turned on and off but after a few days it had stopped working.

So i changed the output back to an LED and still didnt work then i changed the two old school transistors for more recent ones four different ones of the same type and model, the lights work but when the coil is put back i get nothing from the coil but the rest of the lights still light up in their order.

Is there a way to boost the current like a replacement transistor for the darlington pair ( both BC108C's )without increasing the voltage to the circuit?

 

What current is needed for the coil?
Or, what is the resistance of the coil?
Did you use a snubber diode across the coil?

What chip is used to drive the LED's?

 

I have following code. but all leds are fading and getting on together. no running action. how can i make chaser action with fading effect. i mean comet tail. pls help me?



#include <pic.h>
#define FADE_RATE 12
#define INITIAL_WIDTH 128
void fade()
{
unsigned char rate = FADE_RATE;
unsigned char pulse_width = INITIAL_WIDTH;
unsigned char count;
while(pulse_width){
PORTB= 0b11111111;
for(count=0; count<pulse_width; count++){
asm("NOP");
}
PORTB=0b00000000;
for(; count; count++){
asm("NOP");
}
if(!rate--){
pulse_width--;
rate = FADE_RATE;
}
}
}
int main(void) {
char b;
TRISB = 0b00000000;
while(1){
for(b=0x02; b; b<<=1){
PORTB = b;
fade(b>>1);
}
for(b=0x40; b; b>>=1){
PORTB = b;
fade(b<<1);
}
}
}