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| DNA Dan:
What motor are you using? Where did you get it from? |
| DaOld Man:
--- Quote from: danny_galaga on March 21, 2011, 09:36:11 am ---The motor only draws maybe an amp at most, I just realised I could probably keep it even simpler and use a transistor only (",) --- End quote --- You will probably need an H drive (4 power transistors and 4 switch transistors.) You could get away with just two power transistors, but you will need a dual power supply. |
| danny_galaga:
--- Quote from: DaOld Man on March 21, 2011, 05:35:20 pm --- --- Quote from: danny_galaga on March 21, 2011, 09:36:11 am ---The motor only draws maybe an amp at most, I just realised I could probably keep it even simpler and use a transistor only (",) --- End quote --- You will probably need an H drive (4 power transistors and 4 switch transistors.) You could get away with just two power transistors, but you will need a dual power supply. --- End quote --- God yes, I think so linearly! I think of one thing, and forget the other. So amps wise a transistor is fine, but the simplest way to flip/flop for my cab is a relay. How much current does the printer port output with your system? How much for the USB? Only signal-sized outputs? A few milliamps? there are some really small mechanical relays on the market which might just work without amplifying the signal. Otherwise, it's what you said originally- a transistor driving the relay. |
| DaOld Man:
Printer port is good for 10-20 MA. (Most likely 10-15). Usb is good for maximum 500 ma, and sometimes it is only good for 100 MA, so I highly suggest you do not try to directly drive a relay with these ports. However there are drivers out there such as the ULN2823A http://pdf1.alldatasheet.com/datasheet-pdf/view/120808/ALLEGRO/ULN2823A.html that can drive a relay. The only drawback is that it inverts the signal (high from printer or usb port = low at relay), but this is ok for relays, just keep it in mind. They are good for up to 500 ma. But the above link says they have quit manufacturing the ULN2823A. Another option would be to use the H Drive chip that sjbaines used on his project: http://forum.arcadecontrols.com/index.php?topic=107919 (No relays necessary except for degauss, if you need that function). Last but certainly not least you can use an opto-isolator between the port and the relays. |
| DaOld Man:
I threw together this circuit. It is using the RS232 pin 7 (RTS) to turn on a small motor. Opening the comm port causes RTS to go high, which turns on Q1 (a small power transistor) which turns on the motor. Closing the comm port causes RTS to go low, which turns off the motor. I have bread boarded this and it seems to be working fine. The only problem I can see right away is that if another program attempts to open the same comm port, may turn on the motor. This could be your answer to using one relay to switch your motor the same way your DPDT switch is doing now. Just substitute teh motor in the drawing with a relay coil. EDIT: I changed the drawing to show an additional diode, D2. The port when high is +12 VDC to ground. When it goes low it is -12 VDC to ground. D2 keeps the -12 volts from the transistor. The transistor that I used doesnt mind this, but some may. |
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