Re: car blinker circuit?

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There are simple ways, if you know electronics.

An inverter with a resistor across the input and output and a capacitor from
ground to input will oscillate at the output as long as the inverter has
some hysstatsis. If you use 2 resisters and a transistor as the inverter
(pnp emitter ground, two resistors to source from the collector, output
between the resistors, it should work ok.

Of you could just get a 555..... google it and you should hit about 10
billion 555 circuits
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Re: car blinker circuit?



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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.

Re: car blinker circuit?



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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.
--
John G

Wot's Your Real Problem?



Re: car blinker circuit?
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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

Re: car blinker circuit?


put finger to keyboard and composed:

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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.

Re: car blinker circuit?



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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.

6 volt versions were even more critical.

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.
--
John G

Wot's Your Real Problem?



Re: car blinker circuit?


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:

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Re: car blinker circuit?


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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.

Re: car blinker circuit?



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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.
--
John G

Wot's Your Real Problem?



Re: car blinker circuit?


On Thu, 08 Dec 2005 09:43:30 +1100, Clifford Heath

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

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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.

Re: car blinker circuit?


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.

Re: car blinker circuit?


On Thu, 08 Dec 2005 09:43:30 +1100, Clifford Heath

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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.

Re: car blinker circuit?


On Thu, 08 Dec 2005 16:31:55 +1100, Franc Zabkar

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

-- Franc Zabkar

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

Re: car blinker circuit?


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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

Re: car blinker circuit?


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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)

--

Bye.
   Jasen

Re: car blinker circuit?



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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.

Re: car blinker circuit?
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Thanks Andy.
6-volt flasher units can be bought, but only from specialists now.
Supercheap Auto don't have them. etc etc

Jordan

Re: car blinker circuit?
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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

Re: car blinker circuit?
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One would do!

Jordan

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