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Modifying toggle switch to automate delay

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Here's what I have done so far, and questions / comments I have:

  • I have re-directed the caps from the reset pin to go to active power supply. Hopefully I have them around the right way!
  • Diodes quoted in most places are 4148, but I think they should be higher rated (e.g. 4001)
  • The 4004 fly back diodes for the relays are way over spec'd, but the parts library I drew this from does not have lower rated diodes!
  • Not sure if I need a current limiting resistor to feed the base of the transistors. I don't have specs for the relays as yet, but I could assume the base needs at least 1 milliamp to turn it safely on. The Q output only puts out around 3 milliamps.
  • The relay set up might need some explanation. I have used DPDT, using one of the poles (say pole B of relay B) to switch power to pole A of relay A, pole A doing the primary switching to the roof ECU. This is just to ensure that power is not available to the relay that is not being used.

The schematic is probably a bit busy but it passes all circuit tests. I have used Eagle software to do this. Any comments would be welcome. I have tried placing this schematic onto a board in Eagle. Now that is a challenge!
 

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  • roof toggle.pdf
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speedorhaste; You can use 1N4001 for the relay flybacks and 1N4148s for the signal diodes. You should have base resistors probly around 500 ohms. Andy
 
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Thanks. What are the maths to derive 500 ohms for the base resistor? The relay coil resistance is probably around 360 ohm, giving 33 mA current, so the BC547 transistor will drive that just fine. With an Hfe for that tranny of at least 100, 1mA of base current should drive it well enough. The thing I don't understand is the current output from Q on the 4013 and how its moderation by the base resistor is calculated.

Will now be spending some time ensuring I have the existing wiring to the ECU properly identified, then some shopping around for parts and (the bit I hate) placing the parts on a board (despite the help from the Eagle app, it is somewhat tedious).
 
speedorhaste; Generaly you need 1 tenth the current of the collector on the base for proper saterashoin. 500 ohms will get you close.
The thing I don't understand is the current output from Q on the 4013 and how its moderation by the base resistor is calculated
You can think of the output of the 4013 as a switch between power and ground and do the math for the base resister from thare.
Andy
 
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