# small circuit help needed

Discussion in 'Electronic Basics' started by Bob in PHX, Feb 20, 2005.

1. ### Bob in PHXGuest

To All,
I have an interesting problem that I need to solve. I have an older
electronic blackjack machine that has blown the coin hopper pay out circuit.
No schematic of the board is available and the pcb has a 25 cent sized
burned clean through it.... The good part is that I found a chip that puts
out a 5 volt signal when the "jackpot" is hit and the coin hopper needs to
start. This 5volt signal stops when the jackpot has been paid.

I was thinking that a simple relay would work, but then I worried about
pulling to much amperage out of the chip, which by the way is some sort of
specialty chip, thus I don't know what the chip can stand. So, I figure that
I need some sort of opto isolator chip that has a very small amperage draw.
This chip would allow me to use a separate power supply to trigger the
relay, with say a 2n3904 transistor.... I just don't know what chip to use
that would isolate the 5v trigger lead from a separate 5v powered circuit.
The two circuits would not share a ground.

any ideas??????

Bob in phx....

2. ### John FieldsGuest

---
View using a fixed pitch font:

+5V
|
+----+----+
|K |
[1N4001] [COIL]- - -|
| | +--> |
+----+----+ | |
| O O--->TO COIN HOPPER
C |
5V TRIGGER>----[1000R]----B 2N4401 +-------->TO COIN HOPPER
E
|
GND>------------------------+

3. ### Bob in PHXGuest

AWSOME!!!!!!!! Only two questions. What is the [1000r]. I am guessing a
1000 ohm resistor?????

Second, the ground show comes from the second power supply or from the same
ground as the trigger???

Thanks for the design and in advance for the answers to my two questions!!!

Bob in phx

4. ### Rich GriseGuest

For the circuit[0] to work as shown, both grounds (for the trigger source
and for the relay supply) need to be common (connected together). Since
the relay contacts are isolated, it doesn't matter where ground is in the
payout circuit, as long as the difference doesn't break down the relay
insulation, which is very unlikely.

Good Luck!
Rich

[0]

6. ### Bob in PHXGuest

Thanks for all the help... Ill try it out this week and report back the
results!!!!!

Bob in phx