Re: car blinker circuit?

There is a 555 variant specifically targetet at automotive use, cant remember it off the top of my head, but it exists. Personally, if I were you, i would head down to my local supercheap (or similar auto store) and by a generic electronic flasher. It will more that likely work and if it doesn't it wont be hard to modify. I would be surprised if you could not find one targeted for 6V.

BTW, what is wrong with a electro-mech flasher? They have been in use for a very long time, and still are. They must have something going for them.

The thing they have going for them is that they flash at the legally required rate 60-120 flashes per minute and they change rate when a lamp fails (also legally required) indicating to the observant driver that something is amiss.

You will need a 6 volt version because as you already know the current is double for the same light output on 6volt systems. Incandescent lamps should be 18 - 21 watts.

One would do!

Jordan

I've looked, but not found any 6V electronic flasher cans. The standard type of can probably won't be happy to drive LED bulbs, which I want to use, as 6V bulbs are only available to 10 watt, which is marginal I think. And, while blinker cans tend to go bung every coupla years, I thought an electronic solution might last a lot longer. And, I want to be ready when all 6 volt stuff is no longer available.

Thanks Jordan

That's another feature I'd like to have in an electronic blinker can. It's the lack of observant drivers that's convincing me I need blinkers! Haven't seen any 6V, 18-21W bulbs - do they exist?

Thanks Jordan

On Tue, 6 Dec 2005 20:19:23 +1100, "John G" put finger to keyboard and composed:

IIRC the flasher is also required to turn on as soon as the indicator switch is activated. If so, then you can't just switch the output of a free running oscillator.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

Thermal flashers passed the current thru the heater wire and the lamp until the wire was slack enough to let the contact close and short the heater which lit the lamp and allowed the heater to cool and pull the contact open, heat again etc etc. They were very critical of lamp wattage and contact and ground cleanliness.

Recent electronic flasher flash first and then go dark.

As far as I know all switches work on the hot side because almost invariably the lamp holder was metal and screwed to the body and hence grounded.

If you cant figure out a 555, then perhaps you should go with the local auto shop's 6 volt electro-mech version of flasher.

IIRC the OP wanted a circuit that allowed him to have one flasher, but couldn't work out how to do this - the answer is simple in that he just needs to wire the flasher switch from the batt + to one side of each flasher light pair (assuming + earth) and insert the flasher unit from a point that connects all the earth side of the lights to an earth point - ie it goes in the common earth return or the indicator lights.

The above approach also allows for the emergency ALL FLASHING situation by using an EMERGENCY switch that applies + to both pairs of flashers

And this is assuming he can overcome the difficulty posed by John, if that is still the case after converting to LEDs

David

John G wrote:

Have you got a reference for that? Because as noted, the electro-mech ones don't generally do it. I know the one in my car doesn't, and I'd like to fix that without having to build my own. If flashers are now required to do it, I'd have a reason to get a refund on one that didn't :-).

The other problem with most 555 circuits (and the inverter circuit mentioned) is that the first half-cycle takes noticeably longer. A flasher circuit shouldn't do that. Any clever ideas about how to design this behaviour? Apart from the obvious one of using dividers etc...

Clifford Heath.

I do not have a set of regs to help with that and am relying on memory from a previous life.

It has come to my attention that the at least the old regs and I have no reason to think it is changed, An audible signal is required to remind the driver that the flasher is still going and so any attempt to build a flasher from electronics will require the extra components to make the noise.

In short the simple path is a commercial flasher which could likely be obtained thru some vintage car club as there are people with garages full of old stuff that turn up at club days to flog their wares.

Thanks Andy.

Jordan

On Thu, 08 Dec 2005 09:43:30 +1100, Clifford Heath put finger to keyboard and composed:

Sorry, I checked my old ADRs (1982) but couldn't find anything. ADR 6 should cover direction indicators.

I found a writeup for an old magazine project. ETI327 is a turn/hazard indicator with an audio output. It uses two 555s, an audio oscillator and a flasher. The flasher is a free running oscillator, so it looks like I may be wrong. Of course the requirements may have changed since then.

But then there is this info from a Bosch Technical Instruction booklet, "Electronics (2) Automotive Applications".

==================================================================== "German traffic regulations prescribe 60 ... 120 switching cycles per minute as the signalling frequency. The time when the lamps are lit must be between 30 and 80% of the turn signal switching period. For traffic safety reasons, the turn signal should light when first switched on. Furthermore, German traffic regulations prescribe that the failure of one of the turn signal lamps is to be indicated clearly to the driver, for example, by doubling the signaling frequency or by the indicator lamp remaining unlit." ====================================================================

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

On Thu, 08 Dec 2005 09:43:30 +1100, Clifford Heath put finger to keyboard and composed:

The mechanical flashers require that lamp current flows through a bimetallic strip which opens after it heats up. The electrical contact is re-established after the strip cools down. If no current flows at switch on, then what heats the bimetallic strip?

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

On Thu, 08 Dec 2005 16:31:55 +1100, Franc Zabkar put finger to keyboard and composed:

Oops, you wrote "electro-mechanical". Sorry.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

if you're switching the power to the circuit split the timing capacitor between the rails with a 2:1 ratio. put the 2 on top if you want the output to start low (other way up for low)

if you're not switching the power you need a pull-down (or up) to 2/3 (or 1/3) rail voltage in the timing capacitors chip end. while dormant (and it should switch off when it's to wake up)

The lasr mechanical flasher I looked inside operatd by a heater that heats a wire that's stretched across a spring steel gasket. When the wire stretches a little the gasket clicks into a new configuration that closes the contacts and short-circuits the heater element.

I do remeber seing one bimetalic flasher, IIRC it was a bekelite affair and had a heating element wrapped around the bimetallic strip. I think the heated-wire versions are cheaper to make.

Bye. Jasen

Thanks Franc. I got an electronic flasher unit at a local car bits shop, it was no problem at all, unlike last time I tried some years ago. The guy knew exactly what I wanted.