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HowTo: How to build a triac switching unit (SSR)
( Robert Stark)
Step 7 : Controling the whole mess
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| | Let me introduce you to my little friend! This is the ULN2803/2804 octal high voltage Darlington transistor array. The 2803 is for TTL level input signals, the 2804 is for CMOS. This wonderful little chip has 8 channels that can be individually controlled. Each channel will sink up to 50 VDC at up to 500ma (The 500ma is for all channels combined so you have to do a little math if you are switching high current loads). Application of this chip couldn't be easier. The output of any type of controller, whether it be Hill's 300 port controller or the parallel port itself, is connected to pins 1 thru 8. When a signal is applied to the input pin, the corresponding output pin (pins 18 thru 11) is connected to ground. Using this chip as a buffer between your controller and your hardware will allow you to use different types and voltages of SSR boards as well as directly control relays with the same controller.
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