Following on from this answer to a previous question from a while back, I want to add a new lamp (with its own button/switch).

  1. The new lamp should be controlled separately (i.e. not controlled or affected by the timer).

  2. When activated, the new lamp should emit a single flash.

  3. Triggering the flash should interrupt/reset/disable the timer (if it's active), killing the lights.

The idea is to mimic the behaviour of a (photo) flash with auxiliary lighting that automatically cuts out when the flash fires. In reality flash lamps are usually high voltage xenon tubes. But for now I'm more interested in the switching, and the rest of the circuit so I'll just be using a regular incandescent bulb to demonstrate the concept.

20-Second MOSFET Timer 20-Second MOSFET Timer

  • \$\begingroup\$ How long does the flash need to be? \$\endgroup\$ – Trevor_G Nov 9 '17 at 18:31
  • \$\begingroup\$ @Trevor Trevor, mate. I was hoping you'd see this. You really helped me last time. The shorter the better, probably. I think usually anywhere between 1/60 sec - 1/250 sec. But it's not super important at this stage. \$\endgroup\$ – voices Nov 9 '17 at 19:08
  • \$\begingroup\$ Meh forget it, at this point you would be better with a 555 type circuit... \$\endgroup\$ – Trevor_G Nov 9 '17 at 20:01
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    \$\begingroup\$ Discrete means.. uses simple parts like R,C and Q. And yes, a 555 is not the best circuit in the world, because it is still more consistent than discrete parts. Your circuit probably works great on a sample of one. But if you build 100 of them, you will find they are all different. \$\endgroup\$ – Trevor_G Nov 10 '17 at 16:36
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    \$\begingroup\$ I might revisit the discrete version later though.. just for fun ;) \$\endgroup\$ – Trevor_G Nov 10 '17 at 16:37

This really is not a free design service, but since you quoted my answer to your previous question, I'll give you one more freebie.

You could use this simple method.. The switch enables the flash through a cap so it will only be on a short time. D1 and R3 gives the cap a discharge path.

Meanwhile, the switch also pulls the gate of M1 low and discharges C1 through D2, killing your timer.


simulate this circuit – Schematic created using CircuitLab

The flash would not be that bright though since the cap, unless it is very large, will likely charge faster than the lamp can heat up.

However, at this point you would be better to go for something a lot better controlled that gives you some manual adjustments like the 555 (556) circuit below.


simulate this circuit

Or better still use a small mirco that uses electron vapour to run.

| improve this answer | |
  • \$\begingroup\$ Thanks for answering. For the record. I'm not really looking for a free design service. I'm not building a marketable product, and I'm not making a financial profit. I just come here to learn. Like everyone else, I imagine. And this is how I learn; something obscure piques my interest, and I ask weird (sometimes difficult) questions until I gain the understanding I'm looking for. More often than not, I'm met with negativity, ignorance, condescension, and even hostility. But every now and then someone helpful and encouraging will come along and I'll be refreshed and inspired. \$\endgroup\$ – voices Nov 10 '17 at 12:38

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