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
 
On Mon, 12 Dec 2005 15:17:15 +1100, Jordan wrote:

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
Click to expand...
The horn will be putting all sorts of voltage spikes onto your supply
voltage. This is because most horns are a coil (electromagnet) and pair of
contacts. Each time the horn diaphram is attracted to the
electromagnet, it causes the contacts to open, the diaphram then
returns to it's original position allowing the contacts to touch
again. The magnetic field in the coil collapsing as the current is
shut off causes a high voltave spike, it is this series of spikes that is
causing the timer circuit to reset at odd intervals instead of the cycle
rate you have selected by the component values you used.

You would need to filter these spikes out of the supply to the timer chip
to stop this from happpening..... try putting an inductor in the + supply
line, with a cap to neg on the 555 side of the coil. It could also be
worthwhile putting a 17 volt zener accross the cap to help shunt any
remaining spikes to 0v.



+ ---- ciol ------|-------- 555 power input
|
|
--- filter
--- cap
| (17 volt zener in
| parralell if desired)
0v

The inductor in the supply line will try to keep the current into the
filter cap constant, as inductors resist change in the current through
them. The filter cap will smooth out the remaining voltage spike left on
the supply.



Pip
 
Thanks Pippa

I'll try that.
I've not worked with inductors. I see various types - RF chokes, ferrite
coil packs, mini coil packs. Which type should I use?
1 to 1000 uH of the RF chokes available - choice not critical?

I really need to fix this, as I've found that just running the engine
causes the same problem!

Jordan

Pippa Reeves wrote:
On Mon, 12 Dec 2005 15:17:15 +1100, Jordan wrote:


I have it fitted to the vehicle now, working almost normally.
A steady mark/space pulse happens, until I use the horn.


You would need to filter these spikes out of the supply to the timer chip
to stop this from happpening..... try putting an inductor in the + supply
line, with a cap to neg on the 555 side of the coil. It could also be
worthwhile putting a 17 volt zener accross the cap to help shunt any
remaining spikes to 0v.
Click to expand...
 
On Tue, 13 Dec 2005 08:52:38 +1100, Jordan wrote:

Thanks Pippa

I'll try that.
I've not worked with inductors. I see various types - RF chokes, ferrite
coil packs, mini coil packs. Which type should I use?
1 to 1000 uH of the RF chokes available - choice not critical?

I really need to fix this, as I've found that just running the engine
causes the same problem!

Jordan

Pippa Reeves wrote:
On Mon, 12 Dec 2005 15:17:15 +1100, Jordan wrote:


I have it fitted to the vehicle now, working almost normally.
A steady mark/space pulse happens, until I use the horn.


You would need to filter these spikes out of the supply to the timer chip
to stop this from happpening..... try putting an inductor in the + supply
line, with a cap to neg on the 555 side of the coil. It could also be
worthwhile putting a 17 volt zener accross the cap to help shunt any
remaining spikes to 0v.
Click to expand...
Hi Jordan,

something like CAT. NO. LF1272 from Jaycar should do the job nicely. It is
a 100uH rated at 3 amps DC.... I don't know how yoou have the output of
this flasher circuit wired up, so I assumed that you would probably be
running the full load current through the choke.... that's why I suggest
one that is pretty beefy physically and low DC resistance. If the load
current of the lamps is being switched by a FET or bipolar transistor,
relay etc, you may possibly be able to seperate it's current draw from the
supply that is running the 555 and use a physically smaller choke just
filtering the 555 power, but not the lamp supply.


As for the cap, I would throw something like a 220 uF electrolytic, with a
100 nF polyester cap in parralell..... You may ask why the little baby
size cap accross the electrolytic? It is there because the construction of
an electrolytic makes it not very good at filtering very high frequencies,
whereas the little polyseter one, is designed for RF stuff, so has really
good high frequency response. Because the thing you are trying to filter
out is high voltage pulses, these have a very fast rise time, so to a cap
they tend to look like a very high frequency pulse.


None of these component values are really critical.... after all you are
just trying to 'stomp' on high voltage pulses that are superimposed onto
the supply voltage.

have fun,

Pip
 
According to their FAQ:

"Question: Will FlashAlert work on 6V systems?
Answer: No... FlashAlert operates from 8 to 16VDC."

If you say it only affects the audio feature, how do you come to know this?

I'm not sure if Atmel makes the chip for it, but it's the only maker
I've been able to find that makes IC's specifically for electronic
blinker cans, and they also don't support 6V.

Even if it could be used, I might still have the same EMI problem, as
the ignition magneto is unshielded and unsuppressed - I don't want to go
that far.

Thanks
Jordan

Professor wrote:
The Telstar unit will operate the flashing easily down at 6V... but the
audio feedback may or may not function.

Professor
www.telstar-electronics.com
Click to expand...
 
It's nice to be able to talk to the designer.
Do you have any comments regarding Atmel's recommended supply voltage
range (9V to 15V for U643B)?
I'm assuming you're using their IC's.

Jordan

Professor wrote:
How do I come to know this. I'm the designer...

Professor
www.telstar-electronics.com
Click to expand...
 
Actually, the FlashAlert uses the 556 timer chip...

Professor
www.telstar-electronics.com
 
Do you have any filtering on the power source for your circuit?

Professor
www.telstar-electronics.com
 
Yes, I've tried combinations of inductor, zener and various caps - no help.
I can replicate the behaviour by running a spark generator nearby, so I
can bench test instead of starting the engine each time.
I don't suppose you've needed to do such a test? (as you'd be selling to
car owners with properly-suppressed battery/coil ignition systems?)

Jordan

Professor wrote:
Do you have any filtering on the power source for your circuit?

Professor
www.telstar-electronics.com
Click to expand...
 
Send me a drawing/schematic of your circuit.
Have you looked at the B+ power feed with a scope?
How does your circuit fail? Erratic flashing? No flashing? Other?

Professor
www.telstar-electronics.com
 
Drawing is here: http://tinyurl.com/95w5w

I haven't used a scope - I guess that would narrow down where the
interference is affecting the circuit? It happens even with no wired
connection to the vehicle.

Erratic flashing is what happens when the engine's running. It is almost
regular at low revs, but gets very haphazard when the throttle's opened
up. The magneto is probably generating more RFI at higher revs.

Thanks
Jordan

Professor wrote:
Send me a drawing/schematic of your circuit.
Have you looked at the B+ power feed with a scope?
How does your circuit fail? Erratic flashing? No flashing? Other?

Professor
www.telstar-electronics.com
Click to expand...
 
Your circuit looks fine. The thing I might try first is to decrease the
1M resistor to draw more current through the 555. I guess maybe a 10K
and 100uF to maintain your RC time. It's easy to try...

Professor
www.telstar-electronics.com
 
Tried it today - alas no improvement.
I did find out however, that it's quite sensitive to the relative
position of the spark source, so it might be worth trying to relocate
the blinker circuit on the vehicle.

Thanks
Jordan

Professor wrote:
Your circuit looks fine. The thing I might try first is to decrease the
1M resistor to draw more current through the 555. I guess maybe a 10K
and 100uF to maintain your RC time. It's easy to try...

Professor
www.telstar-electronics.com
Click to expand...
 
So you believe it's radiated interference that's causing this
problem... and not junk on the power lead?

Professor
www.telstar-electronics.com
 
I've proved that, by having it completely remotely-powered - not
connected to the vehicle at all. I set up a circuit, with a separate
battery, and put it on a stool nearby. It ran well until I started the
engine.
Of course, it may be that the remote power lead is what is picking up
the radiated interference!

Jordan

Professor wrote:
So you believe it's radiated interference that's causing this
problem... and not junk on the power lead?

Professor
www.telstar-electronics.com
Click to expand...
 
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