This is a multi-part message in MIME format. ------=_NextPart_000_12A9_01C8B90E.9B45C220 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Ok, first, let me just remind everyone that I'm almost totally clueless when it comes to analog electronics. Years ago, I took classes in the Navy on transistors and I sort of understood it... back then... I'm trying to drive a small 5 volt relay from a pin on a PC parallel port. The circuit I'm trying is right out of the PICList archive / FAQ at: http://www.piclist.com/techref/io/relays.htm more specifically at http://www.piclist.com/techref/io/relay9v.gif but it is for a PIC, not the PC parallel port, and certainly not for nStrobe, which is one of the weaker lines on the port. This is probably the cause of my troubles, but I don't know how to fix it. The attached is the actual circuit. RELAY: OMRON G5LE-1 DC5 According to the datasheet: https://www.jameco.com/Jameco/Products/ProdDS/187151.pdf it has a coil resistance of 63 Ohms. I have a 1N4148 connected backward over the coil to prevent kick back. PC: Parallel Port pin 1: nStrobe is the line that I need to use to drive this relay. It is supposed to be driven, in the parallel port hardware, by the equivalent of a 7405 inverting open collector buffer, pulled to +5 volts via a 4.7K resistor. http://www.piclist.com/techref/io/parallel/signals.htm I have a 2N3904 transistor with the emitter connected to ground, the base to the nStrobe signal from the PC parallel port and the collector is connected to the relay coil. The other end of the coil is connected to +5VDC. When the nStrobe line is not connected to the circuit, using a program on the PC to toggle the pin, I can get 0.009 - 5.07 VDC on the pin as read by my multi-meter. When the circuit is connected, and powered up, I get 0.010 - 0.657 VDC and the relay does not close. I attached a potentiometer between the base an +5 and turned it until the relay just activated, then backed it off and tried toggling the nStrobe line. At that point I was able to control the relay from the PC port, but removing the pot and measuring its value showed that it was 203Ohms. Not K Ohms; Ohms. That ain't going to cut it. The parallel port appears undamaged. The relay and transistor do switch and the power supply seems to work ok, but 200 Ohms cannot possibly be ok. I don't understand how that failed to destroy the port... My old PC must have some sort of current limiting built in. I had previously been advised (thank you friend) that I might have better luck in a different configuration using a BC337-40, but that was a different circuit entirely. The point of this new circuit is to avoid the extra cost of the more dear transistor. If I have to use it, so be it, but since I'm totally clueless, I figured I should ask for help before trying anything more. HELP? James Newton: PICList webmaster/Admin mailto:jamesnewton@piclist.com 1-619-652-0593 phone http://www.piclist.com/member/JMN-EFP-786 PIC/PICList FAQ: http://www.piclist.com ------=_NextPart_000_12A9_01C8B90E.9B45C220 Content-Type: image/png; name="relay.PNG" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="relay.PNG" iVBORw0KGgoAAAANSUhEUgAAAVcAAADaCAIAAACdCpb9AAAAAXNSR0IArs4c6QAAAARnQU1BAACx jwv8YQUAAAAgY0hSTQAAeiYAAICEAAD6AAAAgOgAAHUwAADqYAAAOpgAABdwnLpRPAAAGYZJREFU eF7tXVuS7CgOrVnBfM52e0m9rOm/OyuoyTQYCyFAYBmDfW5UdGRnUTIW6Ojogf2v39///hT+/e8/ P//+pzTg8zuMKSsI+oF+chqYZG/8/vnFDzQADbxZAz8fLlD6+WBEecDntxgDHeY0sMje+OuHGMI2 5/DN50P4CbYgfsktZZF7/0YDQIGsBtZZxeMWMOdeRD6A4M8vhYB0e3x/+yw9AwXyVOhZKw2k+Gog v6YpCkQEYQcX/+Wz9gZQACggaeBZu1yDgEABWAIsIdbA+1Ag5ALq4cDjcmHgAkBAIKDXgLN/oECy IV7pEzyBxL33Zto0DHzCMWItANlBVAGLZdTHMcMJLXMwIqf5f1QKgQJAAURMz4+YkBfALn/+LgfH KVdJgQJAAaDA2+sjWxcUfqABaGDXAE0E5D4/zGTABcAFwAUqXEBoInxW/QgoABQACgAFXlYTHlx5 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