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Electrical help re: common earth

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EightBySix:

Hi,

I wonder if someone who is better at electronics than me explain something.

If you have (say) an iPac (gets a voltage and ground from the ps2 cable) and a coin mech that is also powered.
The coin mech needs to be connected to the iPac to send a coin signal.

Do they need to share a common ground?
Do I not then need to get the power from the same source as the iPac? Wont be possible if they are a different voltage - and there maybe wouldnt be enough current to drive both.

Probably missing something here.


mcseforsale:

1.) Yes, you can chain the *SWITCHES* on the coin mech to a common ground on the iPac and their associated connectors for coin1 coin2, etc.  The iPac relies on the ground to see if the switch has been "clicked", or changed state, to tell the PC through the USB port that that associated switch was pushed.
2.) The *LIGHTS* on most older coin doors are usually around 14V.  The iPac can't power that...it's a different type of device and iPac doesn't supply power.  Indeed the iPac gets its power from the USB or PS/2 port of the computer which is usually only 5 or 5.5V and about 500mA. 
3.) Go to Autozone (or your neighborhood auto parts store of choice) and get some 12V bulbs that fit the sockets that you are using on the coin door (my particular door took blade type bulbs, so I got some LED blades off Amazon).  Then, wire *ONLY* the wires from the bulbs to a power header from your PC power supply on yellow/black.  Incidentally, on a PC power supply, where you have a connector for a HD, or floppy (usually labeled P1, P2, etc), yellow is 12v+, black is ground and red is 5.5V+.

Here's an explanation of the pinouts on most modern ATX power supplies:
http://www.scary-terry.com/atxps/atxps.htm


Hope this helps.

AJ



--- Quote from: EightBySix on November 13, 2012, 10:57:32 am ---Hi,

I wonder if someone who is better at electronics than me explain something.

If you have (say) an iPac (gets a voltage and ground from the ps2 cable) and a coin mech that is also powered.
The coin mech needs to be connected to the iPac to send a coin signal.

Do they need to share a common ground?
Do I not then need to get the power from the same source as the iPac? Wont be possible if they are a different voltage - and there maybe wouldnt be enough current to drive both.

Probably missing something here.

--- End quote ---


EightBySix:

Thanks for the detailed answer!

I was trying to generalise though - looks like I got caught out!

Specifically, I've made a coin mech with its own micro controller, that has its own power source and ground. It currently lights an LED for testing, and I want that signal to go to the iPac instead.

I'm thinking they would both need to have reference to a common ground.  :dunno

mcseforsale:

Ahh.  I understand.  I'd check the references over at ultimarc.com.  I'm pretty sure there's a way to power a *FEW* LEDs with it, but I've never done it.  As long as your LEDs are 5V and you wire them to the right polarization, I don't see a problem.  I'm guessing the switch and LED are on different circuits, no?  Or, how about this, an optical coin switch where the LED is on and you have a photoreceptor watching it and when a coin passes by, it switches.  But, then you'd have to do it optically with something like an optiwiz...

hmmm...

AJ



--- Quote from: EightBySix on November 13, 2012, 11:20:22 am ---Thanks for the detailed answer!

I was trying to generalise though - looks like I got caught out!

Specifically, I've made a coin mech with its own micro controller, that has its own power source and ground. It currently lights an LED for testing, and I want that signal to go to the iPac instead.

I'm thinking they would both need to have reference to a common ground.  :dunno

--- End quote ---


mcseforsale:

Here's the answer:

LED HARNESS: (Optional). The LED harness plugs onto the 10-way header on the board. The LEDs are connected to the harness via a removeable plug. This can be disconnected to allow the LEDs to be mounted through a panel. Ensure to note which way round the plug is fitted to the LED. The LEDs can be tested by pressing caps lock, scroll lock and num lock on a pass-thru keyboard. If you have connected the I-PAC to the PC using USB, in mame.ini change "led_mode" from "ps/2" to "usb"

From here:
http://www.ultimarc.com/ipac2.html

AJ

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