Build: Solid State Turn Signal Flasher

The cool new LED turn signals will not flash using a standard flasher that relies on the bulb current to make it flash. This schematic is for a solid state flasher that will work with either LED or bulb turn signals:

U1 is a standard 555 timer set up to "free run" at a frequency of about one cycle per second. You can adjust the flash rate by changing the value of R2. More resistance makes it cycle slower, less resistance makes it cycle faster.

Q1 is a P-FET used as a switch to apply 12V to the turn signals (through the turn signal switch shown in second figure). This particular P-FET has an On resistance of about 70 milli Ohms, so that means it can easily handle the 3A it would take to drive two standard 1157 type bulbs if the stock bulbs are there.

R1 and the zener diode ZD1 are to protect U1 from overvoltage transients which might damage U1. Although the bike or car system regulates at 14V when running, it can have brief voltage spikes. The zener diode will clamp thos to about 15V.

This circuit needs to be powered from a switched 12V source which goes off when the key is turned off, not the battery side of the switch.

Here is a diagram that shows how to connect it:

Hey, that's cool if you want to go the "DIY" route.

Alternatively, you can just buy one of these for about $10:

Skyman wrote:

Hey, that's cool if you want to go the "DIY" route.

Alternatively, you can just buy one of these for about $10:

<br><br>Post edited by: Skyman, at: 2008/03/04 13:44

That's true. I've been in the business a long time and have a lot of spare parts to use up....

I love do it your self custom stuff!!

I imagine that this would work for the hazards as well no?

Where would be the best place to get the components for that flasher unit? And do you have a pic of a completed one?

Qdude wrote:

I love do it your self custom stuff!!

I imagine that this would work for the hazards as well no?

Where would be the best place to get the components for that flasher unit? And do you have a pic of a completed one?

I suppose it would work for hazard flasher as well. I think the hazard switch makes all four lamps flash at once? Doubles the current load to the FET, so you need a good P-FET with on resistance less than about 0.1 Ohm. The one listed above is 0.07 Ohm so it will work.


I get parts from Digi Key but I think they have a $25 minimum order. Places like Fry's sell some FETs and ICs, they might have the parts. radio Shack probably has them but they are such a ripoff I cringe at the thought of what they charge.

I don't have a picture of one built up. As I recall a million years ago, I built it on a small board and then poured epoxy on it to keep it from vibrating the leads off.

I will probably ask Loudvhx about this too, but how hard would it be to make it stop flashing, and just stay on solid, after so many flashes so that it could be a brake light modulator?

Post edited by: kzmason, at: 2008/03/07 21:46

kzmason wrote:

I will probably ask Loudvhx about this too, but how hard would it be to make it stop flashing, and just stay on solid, after so many flashes so that it could be a brake light modulator?<br><br>Post edited by: kzmason, at: 2008/03/07 21:46

I would just use a 556 chip. It's just two 555's in one package. One of the timers would be as Bountyhunter drew it (but with a much faster flash rate for a brake modulator), and the other timer would just be a one-shot timed to about 1 or 2 seconds to stop the flashing. My turn/brake/headlight integrator uses the same circuit, but with a slower flash rate and much longer time-out. But is it worth it, how much do those things cost?

Incidently, the flasher in the above photo (round, translucent case) is only a big RLC timing circuit using a relay, capacitor, and resistor. It's not quite as ideal as a true IC flasher like Bountyhunter's. It has a slight delay before the turn signal comes on, flash rate is still slightly dependent on the load, if the load is very low current, it may not flash at all.

Post edited by: loudhvx, at: 2008/03/08 11:52

loudhvx wrote:

kzmason wrote:

I will probably ask Loudvhx about this too, but how hard would it be to make it stop flashing, and just stay on solid, after so many flashes so that it could be a brake light modulator?<br><br>Post edited by: kzmason, at: 2008/03/07 21:46

I would just use a 556 chip. It's just two 555's in one package. One of the timers would be as Bountyhunter drew it (but with a much faster flash rate for a brake modulator), and the other timer would just be a one-shot timed to about 1 or 2 seconds to stop the flashing. My turn/brake/headlight integrator uses the same circuit, but with a slower flash rate and much longer time-out. But is it worth it, how much do those things cost?

Incidently, the flasher in the above photo (round, translucent case) is only a big RLC timing circuit using a relay, capacitor, and resistor. It's not quite as ideal as a true IC flasher like Bountyhunter's. It has a slight delay before the turn signal comes on, flash rate is still slightly dependent on the load, if the load is very low current, it may not flash at all.<br><br>Post edited by: loudhvx, at: 2008/03/08 11:52

Way back when (about 1984) I built a system to do exactly that. When I applied the brake, both turn signals would flash three times a second for a couple of seconds then go steady on.

I eventually took it off because I got tired of bikers pulling up next to me saying:

"Hey, man..... your turn signals are messed up":laugh:

I like it when they work like old style car tail lights where they go steady on with brake abnd flash for turn signal. Everybody is used to that.

bountyhunter wrote:

I like it when they work like old style car tail lights where they go steady on with brake abnd flash for turn signal. Everybody is used to that.

Same here. Just like my old Dodge Dart.

I learned about those flashers the hard way. They do indeed need a little load to work. One one of my other bikes I did a complete LED swap (gauges too) and they didn't create enough load to fire that kind of flasher.

Coolest car turn signals of all time? Late 60's Cougar, sequential.