Help needed with simple circuit design

[Nick]

Hi all,

I am building a replacement flasher unit for an automotive turn signal
circuit. [The original bulbs are to be replaced with some prototype LED
setups, which cause incorrect flash rates. Now that I'm down this path I
would like to get my design working!] I built a circuit that toggles a relay
at the desired rate... which works great on the test bench.

During fitting, I found that the in-car circuit is different than I first
believed. The flasher unit has power with the ignition on, and the
appropriate bulb circuit is connected by the indicator switch, completing
the circuit to earth. I originally believed that it was the positive that
was switched, and my circuit uses this and a separate earth. In this
configuration the flasher circuit is always active with the ignition switch
on...

I have made a quick circuit diagram of the indicator circuit - please see:
http://202.74.169.80/images/circuit.gif

With reference to the circuit image - The relay shorts "A" and "B" to
activate the turn signals.
My flasher circuit takes power from "A" and "C" [which is no longer
appropriate].

Any suggestions as to how I can power my circuit so it activates with the
turn signal selector? It only requires ~3V and maybe 100mA.

Nick

 

[Mark Jones]

Nick wrote:

Hi all,

I am building a replacement flasher unit for an automotive turn signal
circuit. [The original bulbs are to be replaced with some prototype LED
setups, which cause incorrect flash rates. Now that I'm down this path I
would like to get my design working!] I built a circuit that toggles a relay
at the desired rate... which works great on the test bench.

During fitting, I found that the in-car circuit is different than I first
believed. The flasher unit has power with the ignition on, and the
appropriate bulb circuit is connected by the indicator switch, completing
the circuit to earth. I originally believed that it was the positive that
was switched, and my circuit uses this and a separate earth. In this
configuration the flasher circuit is always active with the ignition switch
on...

I have made a quick circuit diagram of the indicator circuit - please see:
http://202.74.169.80/images/circuit.gif

With reference to the circuit image - The relay shorts "A" and "B" to
activate the turn signals.
My flasher circuit takes power from "A" and "C" [which is no longer
appropriate].

Any suggestions as to how I can power my circuit so it activates with the
turn signal selector? It only requires ~3V and maybe 100mA.

Nick

Hi Nick, how about changing the flasher to a two-lead device? Can you take its
ground lead C and connect it to B?

Short of that, I'm sure one of us can think up a two-or-three transistor
relaxation oscillator to act as a series flasher.

Also don't discount a premade unit, something like:
http://www.ebigchina.com/ebcps/4/pd/459099.html

I changed out my motorcycle's turn signals to LED, and they would not flash
properly with the stock flasher. So I went up to the local car parts store,
bought an "electronic flasher" and plugged it in - presto, problem solved.


-- "Abhorred is the day when it's all figured out." MCJ 200402

 

[Nick]

"Mark Jones" <abuse@127.0.0.1> wrote in message
news:fJudnSjzbJrzYcTfRVn-hg@buckeye-express.com...

Nick wrote:
Hi all,

I am building a replacement flasher unit for an automotive turn signal
circuit. [The original bulbs are to be replaced with some prototype LED
setups, which cause incorrect flash rates. Now that I'm down this path I
would like to get my design working!] I built a circuit that toggles a
relay
at the desired rate... which works great on the test bench.

During fitting, I found that the in-car circuit is different than I
first
believed. The flasher unit has power with the ignition on, and the
appropriate bulb circuit is connected by the indicator switch,
completing
the circuit to earth. I originally believed that it was the positive
that
was switched, and my circuit uses this and a separate earth. In this
configuration the flasher circuit is always active with the ignition
switch
on...

I have made a quick circuit diagram of the indicator circuit - please
see:
http://202.74.169.80/images/circuit.gif

With reference to the circuit image - The relay shorts "A" and "B" to
activate the turn signals.
My flasher circuit takes power from "A" and "C" [which is no longer
appropriate].

Any suggestions as to how I can power my circuit so it activates with
the
turn signal selector? It only requires ~3V and maybe 100mA.

Nick



Hi Nick, how about changing the flasher to a two-lead device? Can you
take its
ground lead C and connect it to B?

Short of that, I'm sure one of us can think up a two-or-three transistor
relaxation oscillator to act as a series flasher.

Also don't discount a premade unit, something like:
http://www.ebigchina.com/ebcps/4/pd/459099.html

I changed out my motorcycle's turn signals to LED, and they would not
flash
properly with the stock flasher. So I went up to the local car parts
store,
bought an "electronic flasher" and plugged it in - presto, problem solved.


-- "Abhorred is the day when it's all figured out." MCJ 200402

Hi Mark,

Yes, that was my first idea... but when the relay shorts "A" and "B" there
is no power to the flasher circuit and the relay drops out... providing
power to the circuit again and pulling the relay in... which shorts the
power to the circuit and.... you get the idea

I was tempted to get an electronic flasher unit, but the circuit uses the
first PIC I have ever programmed (exactly halved the component count from
the 555 version) and I would hate to admit defeat

--Nick

 

[petrus bitbyter]

"Nick" <nick@ineedhits.com> schreef in bericht
news:1113187582.214227@asteroid.globaldial.com...

Hi all,

I am building a replacement flasher unit for an automotive turn signal
circuit. [The original bulbs are to be replaced with some prototype LED
setups, which cause incorrect flash rates. Now that I'm down this path I
would like to get my design working!] I built a circuit that toggles a
relay
at the desired rate... which works great on the test bench.

During fitting, I found that the in-car circuit is different than I first
believed. The flasher unit has power with the ignition on, and the
appropriate bulb circuit is connected by the indicator switch, completing
the circuit to earth. I originally believed that it was the positive that
was switched, and my circuit uses this and a separate earth. In this
configuration the flasher circuit is always active with the ignition
switch
on...

I have made a quick circuit diagram of the indicator circuit - please see:
http://202.74.169.80/images/circuit.gif

With reference to the circuit image - The relay shorts "A" and "B" to
activate the turn signals.
My flasher circuit takes power from "A" and "C" [which is no longer
appropriate].

Any suggestions as to how I can power my circuit so it activates with the
turn signal selector? It only requires ~3V and maybe 100mA.

Nick

Are you sure your LEDs provide enough light? Although LEDs tend to give more
light for the Watt then incandescent bulbs, they are not that much better.
Your LED-load should not be much less then the original lightbulb if it
provides the same amount of light.

Another thing you may take into account is the warning that comes from the
ticking of the thermal flasher. If the load changes due to a failing bulb it
can be heard immediately.

petrus bitbyter

 

[jtaylor]

"Nick" <nick@ineedhits.com> wrote in message
news:1113187582.214227@asteroid.globaldial.com...

Hi all,

I am building a replacement flasher unit for an automotive turn signal
circuit. [The original bulbs are to be replaced with some prototype LED
setups, which cause incorrect flash rates. Now that I'm down this path I
would like to get my design working!] I built a circuit that toggles a
relay
at the desired rate... which works great on the test bench.

During fitting, I found that the in-car circuit is different than I first
believed. The flasher unit has power with the ignition on, and the
appropriate bulb circuit is connected by the indicator switch, completing
the circuit to earth. I originally believed that it was the positive that
was switched, and my circuit uses this and a separate earth. In this
configuration the flasher circuit is always active with the ignition
switch
on...

I have made a quick circuit diagram of the indicator circuit - please see:
http://202.74.169.80/images/circuit.gif

With reference to the circuit image - The relay shorts "A" and "B" to
activate the turn signals.
My flasher circuit takes power from "A" and "C" [which is no longer
appropriate].

Any suggestions as to how I can power my circuit so it activates with the
turn signal selector? It only requires ~3V and maybe 100mA.

I used a relay with a 600-ohm coil and a red flashing LED between the coil
and power.

Low parts count....

 

[Rich Grise]

On Mon, 11 Apr 2005 05:07:54 +0000, Nick wrote:

I was tempted to get an electronic flasher unit, but the circuit uses the
first PIC I have ever programmed (exactly halved the component count from
the 555 version) and I would hate to admit defeat

You've got a PIC? Then you can do anything you want. Put a resistor, say
10K, right from A to B,
http://202.74.169.80/images/circuit.gif
and sense the voltage at B. If it's near ground, turn on the mongo
switch from A to B to turn on the light. After the right delay,
turn off the switch, wait an appropriate "off-time", and check
point B again. If it's low, start the cycle again; if it's high,
idle until it goes low again. Don't look at the voltage on "B"
while the swtiching element is on. ;-)

Have Fun!
Rich

 

[Rich Grise]

On Mon, 11 Apr 2005 17:15:50 +0000, Rich Grise wrote:

On Mon, 11 Apr 2005 05:07:54 +0000, Nick wrote:

I was tempted to get an electronic flasher unit, but the circuit uses
the first PIC I have ever programmed (exactly halved the component count
from the 555 version) and I would hate to admit defeat

You've got a PIC? Then you can do anything you want. Put a resistor, say
10K, right from A to B,
http://202.74.169.80/images/circuit.gif and sense the voltage at B. If
it's near ground, turn on the mongo switch from A to B to turn on the
light. After the right delay, turn off the switch, wait an appropriate
"off-time", and check point B again. If it's low, start the cycle again;
if it's high, idle until it goes low again. Don't look at the voltage on
"B" while the swtiching element is on. ;-)

And for the production unit, when the signals are first turned on, start
a one-minute timer. If after one minute, it's still flashing (i.e., the
lever hasn't been reset), start a very loud annoying beep to remind the
weinerheads to turn off their signal on the freeway. ;-)

Cheers!
Rich

 

[Ross Herbert]

On Mon, 11 Apr 2005 02:51:40 GMT, "Nick" <nick@ineedhits.com> wrote:

Hi all,

I am building a replacement flasher unit for an automotive turn signal
circuit. [The original bulbs are to be replaced with some prototype LED
setups, which cause incorrect flash rates. Now that I'm down this path I
would like to get my design working!] I built a circuit that toggles a relay
at the desired rate... which works great on the test bench.

During fitting, I found that the in-car circuit is different than I first
believed. The flasher unit has power with the ignition on, and the
appropriate bulb circuit is connected by the indicator switch, completing
the circuit to earth. I originally believed that it was the positive that
was switched, and my circuit uses this and a separate earth. In this
configuration the flasher circuit is always active with the ignition switch
on...

I have made a quick circuit diagram of the indicator circuit - please see:
http://202.74.169.80/images/circuit.gif

With reference to the circuit image - The relay shorts "A" and "B" to
activate the turn signals.
My flasher circuit takes power from "A" and "C" [which is no longer
appropriate].

Any suggestions as to how I can power my circuit so it activates with the
turn signal selector? It only requires ~3V and maybe 100mA.

Nick

Hi Nick,

Since you are in WA have you thought about an an Australian made and
approved automotive electronic flasher already on the market here
which are designed for LED lamps and which will provide the functions
required.

Be aware that many so called elctronic flashers are deliberately load
sensitive to cater for normal bulbs. You need a unit which is not load
sensitive such as the 10A and 20A units on this page
http://www.narva.com.au/Switches_24.html

 

Nick <nick@ineedhits.com> wrote:

[The original bulbs are to be replaced with some prototype LED
setups, which cause incorrect flash rates.

Interesting... have you heard of FMVSS 108, ECE-R 48-01, or EEC 76/756?

I
built a circuit that toggles a relay at the desired rate... which works
great on the test bench.

If you have to do something in a hurry, go down to the auto parts store
and buy an "electronic" turn signal flasher. Here, the regular thermal
type costs about US$2, and the electronic type costs about US$10. The
difference is that the electronic type will work over a much wider range
of loads than the thermal type will.

During fitting, I found that the in-car circuit is different than I first
believed. The flasher unit has power with the ignition on, and the
appropriate bulb circuit is connected by the indicator switch, completing
the circuit to earth.

Pretty standard in most cars.

I have made a quick circuit diagram of the indicator circuit - please see:
http://202.74.169.80/images/circuit.gif

What's that thing between point B and the indicator selector?

One idea is to replace the relay with an appropriately rated FET. It
can sit there and switch on and off all it likes, all the time, and you
won't have to hear the clicking. When the indicator switch is turned
on, the switched current will go to the lamps like normal. If you want
to have the clicking noise to remind you that the indicators are on,
wire in a relay coil and leave its contacts open, like this...

2 x LED
o------*----->|---ground
A---FET---B---*--- |
o----*-|----->|---ground
indicator | |
switch | +-->|--+
| *----*-relay coil-*--ground
+---->|--+ | |
2 x 1N4002 +-----|<-----+
1N4002

If you don't want to use a FET, maybe something like this could work,
using the labeled points from your diagram:

A ---*---10K-------------+
| |
| --- |
*---o o---*---220---*--- B
| normally |
| open relay |
| contacts D
|
| relay
+---drive------ C
circuit

The 220 ohm resistor should be replaced by whatever dropping resistor
you need for the LEDs.

With the indicator switch off, B will be open and point D will be pulled
up to battery voltage through the 10K resistor. When the indicator
switch is turned on, this voltage will drop to something like the LED
forward voltage. This is your signal to turn on the drive circuit that
closes and opens the relay contacts. When the relay contacts are closed,
D will still be at the LED forward voltage. When the indicator switch
is turned off again, point D will rise up to battery voltage again, and
you need to shut off the drive circuit.

(Yes, D and B are the same, but it helps the discussion a bit.)

Matt Roberds