car blinker circuit?

I need to put a turn indicator blinker system on my 6 Volt vehicle. I'm looking for a circuit to provide the timed flashing, maybe using a

555 IC. Thought there'd be lots to find, but no. Any reason a 555 can't be used? Anyone know of a suitable circuit? I want to avoid electro-mechanical flasher cans.

Thanks Jordan

Reply to
Jordan
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No circuits? Are you kidding? Search for '555 astable' and if you want to narrow it down more add '50%' to the search terms. Use the output of the astable to drive a MOSFET or relay to drive the lights.

Cheers.

Ken

Reply to
Ken Taylor

Is it OK to have the 555 powered up all the time? I'd prefer if it only got power when the blinker switch is activated. It's refinements like this that I was hoping to find.

Thanks Jordan

Reply to
Jordan

the 555 may not be suited to the wiring layout.

most indicator flashers connect in series with the switch and only start when the bulbs are connected. doing that with a 555 may not be so easy.

also possilby there's a cheaper solution, but for a one off a 555 is plenty cheap enough.

what's the exact aplication (what loads, how is the switch organised)...

what about electro-thermal :)

Are relays no good either?

Bye. Jasen

Reply to
Jasen Betts

I think I've got part of the solution: Use two 555's (or a 556) so that each is energised by the blinker switch, for either left or right. Means some unconventional wiring, but that doesn't matter in this case. Vehicle has no key - ignition is by magneto. So having the blinker arranged this way saves introducing a switch, which I'd be likely to forget to turn off.

Cheers Jordan

Reply to
Jordan

You *could* have the 555 powered all the time, but why not use the switch to apply power to the 555 and the relay/MOSFET/lamps? I don't see the problem.

Cheers.

Ken

Reply to
Ken Taylor

Yes, that's what I've figured out, using the blinker switch, but need to use two 555's unless someone shows me how to do it with one. The only problem is that I'm no electronics whiz!

Thanks Jordan

Reply to
Jordan

Well, I just tried to do some quick ASCII art and it looked crap, so each to his own. :-)

If you have a 'normal' blinker switch, it'll send either the 6V or the ground to the appropriate side of the blinker unit, which then powers the lamps.

For your application, you could use the same switch and use the 6V or gnd to power the 555 circuit and one of the MOSFET's, which would complete the circuit for one set of lamps only. Look at using diodes to power the 555 and only one of the MOSFET's at a time.

Damn, that made bugger all sense to me too - can anyone do a quick bit of ASCII???

Cheers.

Ken

Reply to
Ken Taylor

I understand that, thanks. Will see if I can come up with something. Cost of parts is trivial, but keeping it compact and simple would be good.

Jordan

Reply to
Jordan

They don't use much power I don't see a problem there, connecting it to the ignition switch (or the indicator fuse) would probably be better than direct to the battery.

getting the blink-rate feature could be harder.

Bye. Jasen

Reply to
Jasen Betts

a typical indicator switch is spdt centre off. that's the problem

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   Jasen
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Reply to
Jasen Betts

you can't power up half a 556. making it work with a single chip (and single mosfet etc) would make it more compact

a 555 might be the wrong solution.

an oscilator based around op-amps could sense the dark resistance and vary the blink rate OTOH if he's using LED globes (or panels) they're not going

to fail suddenly. because each panel has multiple LEDs in parallel. so variable blink rate isn't needed

hmmm, this one's compatible with standard wiring and will only run when the lamps are switched on

+-------------+---------------------------+-->from | | /| | indicator | +---------(----[100K]-o< |--------+ | fuse | | | \| | | | | . . . .|. . . . | | | | . VCC(8) . | | | | . . | | +---(---RES(4) OUT(3)-------------||--)---+ | . 555 . || | +---TH(6) DIS(7)-- || | | . . ||--+--->to switch +---TR(2) CV(5)-- p-channel and lamps | . . mosfet --- . GND(1) . 10u~T~ . . . .|. . . . | | +---------+ | ---- //// the inverter could be made from the second half of a 556 etc...

the only problem is it starts off dark and iights up a short time after the switch is turned on

this modification will have it light up immediately when it turned on and then start blinking.

------+---- | /|----(----------+ ---------[100K]-o

Reply to
Jasen Betts

to

the

And just why is that a problem?? Centre off - bravo. Switch to 'left' and power the 555 via a diode and the left 'relay' (or MOSFET, whatever); switch to 'right' and via another diode to the 555 and the relay. Biggus Dealus.

Cheers.

Ken

Reply to
Ken Taylor

Thanks Jasen, that's all interesting but I'm scratching my head a bit. Can you please explain the use of the inverter? Does the circuit "sleep" until the blinker switch is activated? Also, how is a 555 (or half a 556) configured to act as an inverter? I'm slightly more conversant with 555's than with op-amps etc, which is the reason I'm using those. What suggestion is there for a mosfet? I'm using what's at hand here - some MTP3055V's, but these are I think overkill and only show 2.4V instead of the 6V supply voltage. Would a smaller mosfet be likely to saturate and supply the full voltage?

Jordan

Reply to
Jordan

ok. I see now.

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   Jasen
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Reply to
Jasen Betts

yeah that was the idea. it's to get it to sleep

connect reset to Vcc, threshold and trigger are connected together and used as the input, out is a totem-pole output and discharge an open collector output. you get a sort of schmitt inverter.

I don't know much about mosfets. but for a negative earth system (which everyone has assumed without confirming) and switching the live current (which is normal in automotive applications) P-Channel mosfets are best suited. and the range is more limited.

if the MTP3055 has a P-channel brother that would be the one to use

the MTP3055 seems to be trading on the well known 2N3055 bipolar NPN transistors number, and so on a whim entered the 3055's opposite number "2955" into google

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and even that doesn't look promising. I think you're going to need to use a bipolar power transistor. maybe the afforementioned 2955 now available in plastic... TIP2955, that's going to want a siveable base drive so maybe a bd135 to do that (and also function as an inverter)

/ ||/ |/~ +-[22R]-| | |\ | | \ / \ | / | |/ | o-+----- pin3 ----------+---| +----o---- | | |\ 0-)--+-- +->|--+ | \| | | | ~\ +--|

Reply to
Jasen Betts

Thanks for the nice ascii work.

I made something which is running well on the bench. I'm using diodes to select which of two transistors will be powered up, along with the 555, from the blinker switch wired to supply power. I'm bringing out 2 wires to provide a visual indicator that it's flashing - an LED in series from pin 3. It's a bit of a spaghetti junction, with 7 wires coming from my flasher unit:

  1. input left
  2. input right
  3. indicator in (to dash LED)
  4. indicator out
  5. output left
  6. output right
  7. earth

Comments:

- There's a small delay, but not as long as it takes to give a hand signal.

- No lamp failure feature, which would be nice but at least there are no filaments.

- Wiring is not conventional. I'd like to try the suggestion using the inverter, if that makes it more like "standard".

Thanks to all for your help Jordan

Reply to
Jordan

that can be fixed by connecting the timing capacitor to the VCC pin instead of to ground. a diode from ground to the timing pins might be a good idea too in case this capacitor configuration is outside of

| | +-/\/\-----------(---------+ | | | | +---------+ | | | | | | || | . . . .|. . . . | +--||--+ . VCC(8) . | | || | . . | | +---RES(4) OUT(3)---+--- | . 555 . +------+---TH(6) DIS(7)-- | . . +---TR(2) CV(5)-- | . . | . GND(1) . | . . . .|. . . . | | | | +---| - No lamp failure feature, which would be nice but at least there are no

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   Jasen
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Reply to
Jasen Betts

Well, I tried reconnecting the capacitor as per your suggestion, but without the diode (or resistor?), and it works a treat. Now, she starts flashing "on" immediately upon switching. The first flash is very slightly longer in duration - no worries.

Thanks heaps

Jordan

Reply to
Jordan

I have it fitted to the vehicle now, working almost normally. A steady mark/space pulse happens, until I use the horn. Then it goes haywire, with irregular fast flashing. Not a big problem - maybe I should have put in the diode Jasen was talking about.

Jordan

Reply to
Jordan

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