car blinker circuit?

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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

Re: car blinker circuit?
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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



Re: car blinker circuit?


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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

Re: car blinker circuit?
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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

Re: car blinker circuit?
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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

Re: car blinker circuit?
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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

Re: car blinker circuit?
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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

Re: car blinker circuit?
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a typical indicator switch is spdt centre off.
that's the problem

--

Bye.
   Jasen

Re: car blinker circuit?
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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



Re: car blinker circuit?
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ok. I see now.

--

Bye.
   Jasen

Re: car blinker circuit?
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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

Re: car blinker circuit?
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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.

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

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what about electro-thermal :)

Are relays no good either?

Bye.
   Jasen

Re: car blinker circuit?

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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

Re: car blinker circuit?
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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<1|    |          |
                        \|----(-------+  |
          . . . . .           |       |  |
                  .           |       |  |
                  .           |       |  |
            OUT(3)------||----+       |  |
                  .     ||pch       o-|--+----- left signal
                  .     ||            |
                  .     ||---o------  |
                                      |
                 indicator  o-+-------- right signal
                         switch

  the Nor gate could be done with a couple of diodes, a pull-down
  resistor and half a 556.


Bye.
   Jasen

Re: car blinker circuit?


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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

Re: car blinker circuit?
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yeah that was the idea. it's to get it to sleep

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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.

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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

http://www.google.com/search?q=mtp2955+specifications

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-)--+--
          +->|--+   | \|                       |  |
              |           ~\                 +--|<-+  |  
              |             |                |        |
  pin2-[100K]-+-------------(----[1K]--------+--|<----+
                            |      
              -----
                          /////
                            
gotta go - more later.

--

Bye.
   Jasen

Re: car blinker circuit?

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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

Re: car blinker circuit?
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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)    .                                
                      |  . . . .|. . . .                              
                      |         |                                      
                      |         |                                        
                      +---|<----+                            
                                |                                        
                                |                                        
 
     initially-low astable
    
as you may have guessed I have the 555 outline in text file and just
import it and doodle the lines using the keyboard.












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--

Bye.
   Jasen

Re: car blinker circuit?
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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

Re: car blinker circuit?
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

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