wiring a darlington UNL2803

eagle

I am a total newbie at this and would appreciate any help. I have placed my Basic Stamp rev. J P15 to pin 1 on the Darlington and the +out at pin 18.
The 6 volt power supply is + on pin 10 and -at pin 9. I cannot get it to activate a Radio Shack reed 5VDC reed relay.
The relay works well without the Darlington.

Chris Savage

Eagle,

You show your positive supply connected to pin 10, but it also need to connect to one side of the relay coil. Also, your supply for the relay needs to have a common ground with the BASIC Stamp supply (VSS). I can’t tell if you have a + symbol next to OUT1 (pin 18), but that pin will connect to ground when the IN1 pin (from P15) goes high. I hope this helps. Take care.

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Chris Savage
Parallax Engineering

Franklin

Make sure the relay is using the same ground as all the rest. The stamp should be connected to ground and the pin to the 2803. The relay should be between Ground and pin 18. Test with a meter if you have problems.

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- Stephen

eagle

Thanks you, I am going to wire to your suggestions.

Chris Savage

Franklin said...
Make sure the relay is using the same ground as all the rest. The stamp should be connected to ground and the pin to the 2803. The relay should be between Ground and pin 18. Test with a meter if you have problems.

Franklin,

·· With a Darlington the Relay would not be connected between ground and the output.· A darlington will provide a path to ground, sinking the output when the input (base) is high.· When the input is low the output is open-collector.· The relay would be connected between its positive supply and the output of the darlington.· This way when the darlington is enabled it completes the relay's path to ground.· The Nuts & Volts article below should help.

http://www.parallax.com/Portals/0/Downloads/docs/cols/nv/vol1/col/nv6.pdf


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Chris Savage
Parallax Engineering

eagle

Thanks all, it works like a charm.

erco

Those RS 5V reed relays only draw 20 mA, so you can drive them directly from the stamp pins, without any driver transistor at all. And you can turn on 2 of them per 8 i/o pins simultaneously without taxing the stamp's max current limit. Best (conservative) bet is to hook them up between the Vdd (+5) and an i/o pin, since the stamps can sink 25 mA but only source 20 mA. So you make the pin high to turn the relay off and low to turn the relay on. In this manner you can drive 4 relays at once with a BS2, or two relays with a BS1.

The homework & project boards WON'T work since they have inline 220 ohm resistors on all of the i/o pins.

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·"If you build it, they will come."

Chris Savage

As an inductive device, I urge anyone trying to drive one off an I/O pin to add the protective diode across the relay terminal. We always recommend a transistor for many reasons. Insurance like this is very inexpensive and consumes little real-estate in projects.

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Chris Savage
Parallax Engineering