Thanks for this Chris. I will have a look for some information on the IC you have used in this circuit so I can find which pins I need to connect to. Unless you fancy saving me some legwork... ;)
Mark
Hi, Mark. Novice and newbie questions always welcome here.
If you've got half of a CMOS inverter IC (4000-series would include
4049, 4069, 40106, 74C-series include 74C04, 74C14, &c) or three gates you can set up as inverters (NAND, NOR, &c), this circuit might fill the bill (view in fixed font or Notepad):
~ Logic Toggle Pushbutton With Power-On Reset ~ VCC VCC ~ + + ~ | | ~ 1N4002| | ~ VCC - C| ~ + ___ ^ C| RY1 ~ | .----------|___|--------. | C| ~.33uF | | 22K | | | ~ --- | | '---o ~ --- 1N4002| | | ~ | |\\ | |\\ |\\ | ___ |/ ~ o--| >O--|O---o----| >O--o--|___|-o-| Q1 ~ | |/ | |/ | |/ 22K | |>
~ .-. | .-. .-. | ~ 10K | | | 220K| | | | | ~ | | | | | 22K| | | ~ '-' | T '-' '-' | ~ | | --- | || | | ~ | '--o o-------o----||----. === === ~ === || | GND GND ~ GND SW1 .022uF | ~ | | === GND created by Andy´s ASCII-Circuit v1.24.140803 Beta
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Make sure you use a darlington NPN transistor (like the TIP120) to switch the relay. This keeps the load on the last inverter down to around 1mA or so, which any CMOS inverter can handle at 12V. This should be good for any relay coil that draws less than half an amp.
The first inverter with the diode is set up as MML (Mickey Mouse Logic). It's only active at turn-on, and forces the input of the second inverter to be low right after turn-on. That means the third inverter will be low, and your transistor will be off. After a period set by the R and C (something on the order of 3ms) the output of the first inverter will be high, and the diode will effectively remove it from the circuit.
This stuff was borrowed piecemeal from Don Lancaster's CMOS Cookbook, which is a good intro to digital electronics for newbies. It's available at Amazon, libraries, and Mr. Lancaster's website:
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Good luck Chris