I thought it was time to freshen up my police flasher page. After I made the first couple of flashers I learned that it was a good idea to include a larger capacitor on the supply rail. And I don't know what I was thinking back in 2010...not putting caps on the in- and output of a regulator. Well...now I know that it is of course mandatory to put caps on the regulators. Flasher 2 did eventually get a 100uF on the supply rail which help a lot.
Flasher 4 and 5 are the newest designs. Flasher 4 uses only one 4093 and in flasher 5 I have returned to the good old 4017 counter.
Flasher 5 (PF5)
This is the final non micro controller based flasher design. With this design I add the a jumper so that two flash patterns can be selected. Without the jumper the are 3 short flashes and with the jumper 3 short and 1 long flash. The two patterns can be seen on the two ocsilloscope plots.
I have again returned to the 4017 for this final flasher. Again I had 3 spare NAND gates...so why not use them for something.
Here you can see flasher 5 pattern 1.
Here you can see flasher 5 pattern 2.
Flasher 4 (PF4)
This is the absolute simplest design I can come up with. In this design I only use one 4093 quad NAND gate. Two NAND gates are used as oscillators one fast and one slow. A third NAND gate combines the two oscillator frequencies and the last NAND gate inverts the combined signal and sends it to the MOSFET.
The only thing that I do not like about this circuit is the pulse. On the oscilloscope it is clear that the pulse-train is not uniform. This is because the two oscillators are not in any way synchronized. But I can live with that since it only uses one IC.
Here you can see flasher 4.
Flasher 3 (PF3)
Version 3 is still on of the best I did. This was again a 4017 counter and an oscillator but this time only 3 LEDs. Again more caps should have been used. But it works fine.
After this flasher I figured why not try to make it even simpler. Also having 3 unused NAND gates...that was just stupid.
Here you can see flasher 3.
Flasher 2 (PF2)
This version was the big one with both blue and red LEDs I got from China. I switched to MOSFET instead of using BJTs because they are easier to control. This circuit worked very well and is still working. I did have to add some extra capacitor on the supply so that enough power could be delivered to the LEDs. The flash pattern was a little more complex as can be seen in the schematic.
I wanted to make a smaller PCB and just use 2 or 3 LEDs. This lead to version 3.
Here you can see flasher 2.
Flasher 1 (PF1)
This is the first police flasher circuit I did. There are a lot of police flasher circuits out there and this is based on the most common one I could find.
By using a 4017 counter and some diodes you can get a nice flash pattern. The 4017 (U1) is a simple counter and by applying a clock signal (U2) it just keeps running in a circle. By using the diodes (D1/D2 and D3/D4) as an OR gate a flash pattern can be made.
I wanted a more powerful flash and decided to get some other LEDs. I stayed with the 4017 design but switched to MOSFET transistors in the PF2 flasher.
Here you can see the first police flasher.