924Board.org

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

I just found this-Will it work?
Quote is taken from the below source:

You could adjust the value of the 100k resistor to change the RPM setting. This should work, as when the engine is running at too low an RPM the 555 will time out before the next input pulse.

http://www.electronic-circuits-diagrams.com/forum/viewtopic.php?t=66&sid=8d7012bacb798ec1f4e327a62660b092

http://www.electronics123.com/amazon/catalogue/c3-3-11.htm
_________________
1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

Sleykin · Posted: Mon Nov 08, 2004 3:23 pm Post subject:

Unless I am mistaken this circuit will give you a blinking light below a certain input frequency and a steady light if the frequency goes above the set point. Let me dig out some of my old "cookbooks" and see if I don't have a circuit for you.
_________________
Glenn Neff
Medford, OR
87' 924S

Lizard · Posted: Mon Nov 08, 2004 3:41 pm Post subject:

leadfoot · Posted: Wed Nov 10, 2004 7:38 pm Post subject:

You will have a steady stream of incoming pulses with no break, there may be better ways of doing this but you could run the square wave signal from the tach into an opto isolator(so that only signal passes, run this signal through a bandpass filter and use this to trigger a flip flop arrangement(simple 555 timer circuit) driving an led or globe. This with pulse the led, also this timing can be altered by running it through a logic gate to slow down the pulse counting...
For the bandpass filter you can use the example of a parametric equaliser. This circuit will also give you an adjustable Q and centre frequency shift, allowing you to tune into the desired trigger frequency by narrowing the bandwidth, you can just ignore the amplification of this circuit by not running it through the feedback resistor arrangment.
Leadfoot

MunkPuppy · Posted: Thu Nov 11, 2004 10:11 am Post subject:

if you really want a simple alternative for a tach shift light, you could always put in a little wire that contacts teh tach needle at a certain RPM. Of course, doing that would require disassembly of your tach, and teh possibility of it never working again

It is my understanding that you need a circuit that will trigger a light when it recieves pulses that are less than x milliseconds apart. Obviously, the circuit must know to keep the light off when the pulses are greater than x ms apart. I'm no electronics guy, but my brother is an electronics tech and designer. I'm sure he'll have an idea or 2 on how this can be done. Seems to me like it would be a simple timing circuit probably requiring minimal components.
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'80 931 FOR SALE

"It's a shame that stupidity isn't painful"
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Sleykin · Posted: Thu Nov 11, 2004 10:43 am Post subject:

Ah that would be the key

I was locked on frequency but the frequency is so low (200 pps @ 6Krpm) Just put an R/C integrator inline with the circuit and an astable multivibrator with adjustable re-trigger point. That 555 circuit would do this with mods. 3200RPM would be about 37.5ms between triggers etc. If you wanted 3 different trigger points just switch the R's of the R/C circuit. Do a google search on 555 IC timer circuits and I bet you come up with some good stuff.
I looked for the books I thought I still had around but they are gone I guess. 555/556 used to be the main ingredient to a lot of cool projects.
_________________
Glenn Neff
Medford, OR
87' 924S

Sleykin · Posted: Thu Nov 11, 2004 2:34 pm Post subject:

Should have said monostable. Check out this site for info.
http://www.uoguelph.ca/~antoon/gadgets/555/555.html
_________________
Glenn Neff
Medford, OR
87' 924S

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

Wow, You guys are great.
I'm getting closer.
I'm going to arrange a test kit tommorrow.
Tell me if I'm getting it

An r/c adapter changes the square wave signal put out by the coil into a signal

http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/experiment/integ/int.html

http://www.web-tronics.com/moc3010.html

Then I put the 555 timer with a resistor (trigger voltage )
And capacitor (time trigger is set)

questions are :

Where can I adapt to 12 volts for the globe ?(can that be the v+ voltage in figure 9a?)
http://www.uoguelph.ca/~antoon/gadgets/555/555.html

How do you figure 3200RPM would be about 37.5ms between triggers etc?
How is this done using resistors.I thought the resistor was ohms or impedance.I'm confused.
Can I put a pot in place of the resistor for testing?
Is there a adjustable (pot?)for the capacitor so I can experiment and find the right settings?
I"m looking forward to testing the circuit tomorrow
_________________
1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

Sleykin · Posted: Sat Nov 13, 2004 1:12 pm Post subject:

A 4 cylinder 4 stroke engine fires 2 times per revolution. 600 RPM is 20 PPS. Just do the math for the RPM you want. Frequency is the reciprocal of time.
The cap and resister work in conjunction with the timing circuit. The resistance changes the time it take for the capacitor to charge/discharge. The R/C time constant can be varied by changing either R or C. Use a pot for R and you should be able to change the timing to what you want. As long as you pick a suitable capacitance to allow you to get in the range you are shooting for.
I don't think you will need the opto isolator. I would use an LED instead of a 12V lamp. The 555 will easily drive an LED.
_________________
Glenn Neff
Medford, OR
87' 924S

Sleykin · Posted: Sat Nov 13, 2004 1:16 pm Post subject:

Oh .. forgot .. yes you are getting close

The R/C integrator page you mentioned is just right. Adjust the numbers till you get a nice sharp curve at the frequency you intend to run.
_________________
Glenn Neff
Medford, OR
87' 924S

leadfoot · Posted: Sat Nov 13, 2004 5:13 pm Post subject:

The 555 counter could be used to trigger a 555 flip flop arrangement that could be used to trigger a relay in two passes, one accelerating (on) and one deccelerating (off).
Or the counter could be also tied to the reset line so that it resets after each on triggering.
Just thinking out loud....
Leadfoot

Sleykin · Posted: Sat Nov 13, 2004 6:57 pm Post subject:

The monostable configuration will turn the light on steady as long as the input frequency is above the set point. When it drops below the triger point it will go out.
_________________
Glenn Neff
Medford, OR
87' 924S

leadfoot · Posted: Sat Nov 13, 2004 10:08 pm Post subject:

yep i got ya, a schmitt trigger could be used to clean up the input if it's to noisy, digital logic can be run of 12volts , input charge time can be variable rpm through a potentiometer, and leds could be run of output pin and also pin 7 as an auxillary, or possibly run a bi colour led for something funky
Very cool...
If you use a 556 then both input filtering and timing flip flop can be run from the same IC. Just add a relay if you want 12v lamp
leadfoot

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

I picked the the "3" 556 and am going to run the input filter(schmitt trigger ) and timing flip flop on each one.Also I got a 3 color LED with ,green, yellow, red. This will eliminate the problem of multiple lights and gear identification (Great Idea Leadfoot!) each 556 will have a seperate trigger timing and color, 1st gear green ,2nd yellow,3rd red.

Also (great webpage Sleykin!!)The problem is I can't seem to get one test to work on my breadboard.I'm trying to ground the trigger to get a pulse to work but no go.
I'm using a 5volt cell phone adapter for volts.
I think I have the wrong type of capacitor.
Can you guys help me with a resistor and capacitor type (specs) to get this test kit going? My led is forward voltage 2.5 reverse voltage 4v.I don't want to blow it out so I have a multi-tester to check the output pulse.
I still have not figured out the ratio for getting resistance to rpm value Sleykin.
See experiment 11a as a reference.I need values closer to what I am doing than this experiment shows. A 2 sec pulse will be ideal
http://www.uoguelph.ca/~antoon/gadgets/555/555.html

_________________
1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

Sleykin · Posted: Mon Nov 15, 2004 4:26 am Post subject:

Try a 10K pot and a 2uF capacitor. Should get close to a 2 sec pulse unless I am too rusty on my R/C theory (definit posibility) ... Radio shack used to sell Caps and resistors in an assortment pack and it is way cheaper to buy a bunch that way than individual parts. Get an assortment of small electrolitics and some smaller ceramics. You shouldn't need tantilums unless size is a factor. For your experiments set up one 555 as an oscilator with a variable output from 20 to 200 PPS to simulate the ignition pulses. Make sure your cell phone charger (wall wart) has a DC output and add about 20-50 uF cap across it to filter your output. A 9v transistor battery would be a better option for experimenting. You can use an LM7505 IC regulator to get a good 5v source in the car. (again that 7505 number is relying on old grey matter) You are definitly going the right direction with the braedboard.
Don't let the smoke get out

_________________
Glenn Neff
Medford, OR
87' 924S