FLASHER /BEEPER...siiigh

[AnalogKid]

Les:
1. You're right. Somewhere there was a statement about a ground being available and I magically applied that to the center of the switch. Fortunately, not a big change, and the rest of the circuit and the operating theory are all the same.

2. You're wrong, and I knew this would cause problems. The ground symbol in the schematic is *not* the car frame or battery - terminal or anything in the vehicle. It is the reference potential for the circuit only, on perf board, in a plastic box, isolated from the vehicle ground by the switch and one diode (D1 or D2). While no one is trained this way, there is no functional difference between turning something on and off by switching the DC return as opposed to the DC source - as long as you keep the internal and external grounds galvanically isolated except for the switch connection.

Corrected and final (???) schematic to come.

ak

 

[AnalogKid]

OK, lets try this again.

Here's some fun. I got rid of Q1 and R2 by having the two turn signal diodes provide power to the circuit. When both turn signals are off, the 555 has no 12 V so it is unpowered; hence, no output. R1 maintains a minimum resistance between the 555 power pins so they don't float apart (voltagewise) or take transient hit. When either D1 or D2 is powered through the turn signal switch, the circuit wakes up and oscillates as above.

In the previous schematic, a valid state was the 555 powered up but inhibited by holding Reset low. In this state the 555 output is low, so the beeper and LED were connected such that they did not operate in this state. The problem is that a standard 555 astable circuit has a minimum duty cycle of 50%, and as you change the timing resistors it gets larger. That means that when running, the beeper would be on for 10 s and off for 0.5 s, the opposite of what is needed. This is why there was a diode across one of the resistors, to change the duty cycle to 10%.

Now that the idle condition is eliminated, we can "turn over" the 555 output connections. The 555 is enabled all the time when it has power, the beeper and LED are on when the output is low, and the standard astable circuit easily achieves a 95% duty cycle without the diode. This is done by swapping the two timing resistors.

Also, Les pointed out that I had the power connections wrong. This circuit assumes the turn signal switch supplies vehicle power (+12 Vdc) to the circuit.

555 calculator: http://www.ohmslawcalculator.com/555-astable-calculator

ak

 

[Les Jones]

Hi ak,
Your curcuit does not behave the way I understood that kimbear wanted it to behave. My undersanding was the he wanted a delay of 10 seconds before the bleeper amd the LED began to pulse. I then thought he wanted it to pulse at something like 1 Hz. (At about 50% duty cycle.) Although your circuit does not behave like this I think it will be less anoying. My understanding is that your circuit will do nothing for 10 seconds (As requested) but then it will pulse the bleeper and LED on for about one second and continue to do this every 10 seconds.

Les.

 

[AnalogKid]

DerStrom pointed out that something that blares continuously after only 10 seconds would be pretty annoying when sitting in a left turn late for a full minute. I agreed with him. Also, I did a similar circuit a year ago and that thread started with the same idea - a periodic gentle reminder is better than a spanking. Of course, anyone is free to adapt or modify or (heaven forbid) reject any of my posted wonderfulness.

ak

 

[kimbear]

LOL...wow, I didn't think that this would offer so many variances. Analogue, its a simple, elegant circuit that I will be protyping soon.
Analogue Ive changed the parameters, and was wondering if a slight change could be implemented. After finishing tearing apart my covers on my steering column, only to find the wiring is heavily encased in a metal tube, and the turn switch is fully encased....aaaah crap.
There is plenty of room fore a magnet on the base of the turn signal switch shaft, and 2 reed switches on either side of shaft.
So I think Ill be powering this from a 9v battery, and keeping it all self contained.
Can the circuit be powered by a 9vdc battery?
Thanks analogue

 

[AnalogKid]

Sure. Replace D1 and D2 with the switches, and connect both anodes to the +9V. Also, without the timing diode the timing resistor values change to 22K and 270K.

ak

 

[kimbear]

OK, I think I screwed up somehow....

I built the circuit in post #22,,, but it behaves exactly opposite of the way I wanted it to work.

I made it self-contained, running from a 9v battery, with a magnet mounted on the stem at the base of the turn signal arm.
2 reed relays are at the top and bottom of the left and right hand throw of the signal arm, activated when the arm reaches the top or bottom of its throw.

When either of the reed switches are activated, the alarm turns off
but when they are not actuated, the alarm beeps after a delay.

What have I done wrong now???
Man...do I feel like a clunkhead!

heeeeellllllppppp!

 

[DerStrom8]

What reed switch did you use (please provide a datasheet)?

It sounds like you may be using a normally-closed switch when you should be using a normally-open switch.

 

[kimbear]

Actually, at this stage I'm just using test probes to simulate the switch

 

[kimbear]

ACTUALLY...I made a mistake...
fancy that...happens once every couple of years or so...lol
IT WORKS!!!!
And all the timing is perfect as well.
TAHANKS analogue, and all the others that were so helpful...I truly appreciate it