Main > Main Forum
12 volt coin counter with I-Pac/4
clhug:
Okay, I'll give that a try. Maybe I'll try like just a 100 ohm resistor or something.
The nice thing about this relay is it is small, and doesn't make any noise at all. In this case I'm not sure power is a concern. I can see that it could be fallable someday though with enough use. I do agree, I'd kind of rather not have any moving parts that could fail, but it seemed to work pretty flawlessly for now.
clhug:
Okay, I hooked this back up and took some readings. V_BE always seems to be about 0.8 V, but V_CE was 6.5 V when using the 2.2k ohm resistor on the base.
I didn't have any other resistors around at the moment, but I got the idea to use the relay coil as a resistor just to give it a try. It's 250 ohms. With that, V_CE dropped to 4.6 V. So definitely the smaller resistance is giving more voltage through the CE. Does this info help determine at all what size resistor I might need, or confirm for sure whether or not I even need the resistor? (I know it's only 79 cents, but I don't want to potentially deliberately blow the transistor if I don't have to.)
Or worst case, what if I do eliminate the resistor entirely and it still doesn't work? Is there a different type of transistor that would trigger more easily?
Or am I maybe looking at the darlington pair idea again?
clhug:
We have a WINNER!!! I stopped at Radio Shack on the way home from work again tonight and picked up some 100 ohm, 47 ohm, and 10 ohm resistors. I decided to try several instead of just one. Hit it first time. With the 100 ohm resitor on the base of the transistor the counter fires great! V_CE is 1.7 V.
So my question is, should I just stick with the 100 ohm resistor or should I see if there's a higher one that will still work so I have less current that might have less "wear and tear" on the components, if that kind of thing matters at all. Or just not worry about it?
MonMotha:
Don't worry about it. 100 ohms is just fine. In pulsed service like that, the base of the transistor can take a lot of current. I was mostly going through the design for academic reasons (so that you'd know how it's working, or if someone in the future happens upon this thread). If it isn't reliable, you could even go lower. That transistor is actually spec'd for V_BE max of 6V, which seems unusually high to me, but then I'm not normally using transistors in this manner (I'm normally using them linearly as amps). This means that in theory no resistor on the base would be fine.
clhug:
Cool. Thanks for all your help! Now I've just to permanently build the circuit to work with all 4 inputs. Once I'm sure it's working entirely as expected I'll post back my final design for anybody else who may need to do this.
One thing I just thought of today. With trying to trigger the one counter from multiple inputs, if coins are triggered at the same time on different inputs, the counter will only count one unit. This is probably highly unlikely (though possible) if using actual coin mechs, but for someone using coin buttons on their control panel I can see where one player might hold the button down slightly longer while another player is also pressing their coin button. Not sure there's any way around this though. It just seems like something we have to accept when trying to drive it off multiple inputs.