555 timer based flasher "noise" problem

[oldcarman]

I built a simple 555 based flasher to operate in an antique car (6
volt, positive ground) for a turn signal system set for about 1 flash
every second. The "dash" indicator is an LED and all turn signals on
the fenders are led arrays. It works fine on the bench with 6 volt
batteries, but when I hooked it up to the car electrical system using
the chassis for the positive connection and the engine running, the
flashing was totally "high frequency". When I power it directly from
the AA batteries, with the positive lead provided by the chassis to
each LED array on the fenders, the flash is almost the design
frequency, but the time between flashes is erratic. I even get
interference if I don't use the chassis for one lead to the fender
lights. The car has a new 6 v positive ground alternator.

I have tried a few basic capacitor filters (e.g., 0.1 and 0.01uf,
polarized electrolytic) across the power feed at the circuit board, and
non electrolytic on pin 5 of the 555, with no success.

I suspect it is ignition noise. Any suggestions on a filter design for
the flasher circuit? Shield the 555 with metal foil? other?

 

[jasen]

I built a simple 555 based flasher to operate in an antique car (6
volt, positive ground) for a turn signal system set for about 1 flash
every second. The "dash" indicator is an LED and all turn signals on
the fenders are led arrays. It works fine on the bench with 6 volt
batteries, but when I hooked it up to the car electrical system using
the chassis for the positive connection and the engine running, the
flashing was totally "high frequency". When I power it directly from
the AA batteries, with the positive lead provided by the chassis to
each LED array on the fenders, the flash is almost the design
frequency, but the time between flashes is erratic. I even get
interference if I don't use the chassis for one lead to the fender
lights. The car has a new 6 v positive ground alternator.

a guy in aus.electronics had a similar problem.

I have tried a few basic capacitor filters (e.g., 0.1 and 0.01uf,
polarized electrolytic) across the power feed at the circuit board, and
non electrolytic on pin 5 of the 555, with no success.

he tried that too. replacing the 555 with a different brand worked for him.

I suspect it is ignition noise. Any suggestions on a filter design for
the flasher circuit? Shield the 555 with metal foil? other?

maybe try this:


0V ----[10R]--+------+-------+
| | | to LEDs
| | | .---
| 10n| ---- |/
10u===== === 555 ------| NPN
| | ---- |\|
| | | ~|
-6V-----------+------+-------+---------+


also what size resistors are you using to set the speed?


Bye.
Jasen

 

[oldcarman]

Thanks for the reply. I will check that.

I am using 4.7K and 1 meg with a 1uf cap. for the time constant.

 

[jasen]

Thanks for the reply. I will check that.

I am using 4.7K and 1 meg with a 1uf cap. for the time constant.

try 47 ohms 10K and 100uF it should run about the same speed and be less
effected by electrical noise.
mount the capacitor as close to the chip as possible

 

[oldcarman]

1000 uF electro. plus 0.1 uF on 555 pin 1 and 8 solves the problem
provided I stay with AA battery supply, not car system.


Thanks to all who replied!

 

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I built a simple 555 based flasher to operate in an antique car (6
volt, positive ground) for a turn signal system set for about 1 flash
every second. The "dash" indicator is an LED and all turn signals on
the fenders are led arrays. It works fine on the bench with 6 volt
batteries, but when I hooked it up to the car electrical system using
the chassis for the positive connection and the engine running, the
flashing was totally "high frequency". When I power it directly from
the AA batteries, with the positive lead provided by the chassis to
each LED array on the fenders, the flash is almost the design
frequency, but the time between flashes is erratic. I even get
interference if I don't use the chassis for one lead to the fender
lights. The car has a new 6 v positive ground alternator.

I have tried a few basic capacitor filters (e.g., 0.1 and 0.01uf,
polarized electrolytic) across the power feed at the circuit board, and
non electrolytic on pin 5 of the 555, with no success.

I suspect it is ignition noise. Any suggestions on a filter design for
the flasher circuit? Shield the 555 with metal foil? other?

WHAT??!! You're not using the ORIGINAL-type turn-signal lamps, on an
antique car??!!

Ha. Just kidding.

- Tom Gootee

"He who lives in a glass house should not invite he who is without
sin."