Speed-limit Alert PLEASE HELP!!!!!!!!

[pieterw0]

Hi guys

I am new to this forum and hope I can get some assistance.
I recently discovered the Electronics lab web site and decided to build the Speed Alert. The project is finish but has a problem. Still on the work bench, when I attach the battery the beeper and the LED working together lights and sounds on a per second bases. (As it should when it detects the set speed)
I have double checked my pc board, components, tracks and all. I can’t find the problem.
It is possible that I could have made an unknown error with the layout of the board.
Is there someone that could assist me in this regard.
Or perhaps offer an existing pc board layout that is working. Alternatively I will post the layout I have made, if it will help.

Thanks in advance
Pieter

[audioguru]

Hi Pieter,
Welcome to our forum. ;D
I found our project here:
http://www.electronics-lab.com/projects/automotive/004/index.html

Did you sustitute any parts?
Which opamp did you use?
Please post your pcb layout and component mounting layout.
The schematic is here:

[pieterw0]

Thanks for responding

Yep this is the one.

No I have not substituted any parts. For R9 I have used 470 ohm and R20 150 ohm. What does concern me is the IC4069 layout. I could be wrong there but i'm not sure.

IC1 = TL061CN
IC2 = CD4069UBE
IC3 = CD4098BE

Transistors = BC238B

All the other parts are standard.

I still have a gut feeling that the pc board layout could have a flaw but I can't see it.

Thanks
Pieter

(The two holes above R16 is for a bridge)

[pieterw0]

audioguru

Just to confirm! The common or third legs of R8 and R11 is conected (Wiper function). R8 and R11 is both mounted on the project box for easy acsess.
I have checked the Pcboard layout again.

Pieter

[audioguru]

Hi Pieter,
Yeah, pots work better when they are wired as pots. ;D

I checked everything OK up to the 2nd half of the 4098.
Does the 1st LED flicker OK with the sparks?

[pieterw0]

Hi audioguru

What happens is this.
When I attach the power D1 lights up and stays on. D5 flashes and the buzzer sounds on a per second basis. This all happens until I disconnect the battery or when I switch the unit off.

So if you recon that the Pc board is ok then that means that the circuit is wrong.

I would really like to make this circuit work. Do you know of any one that has built this project with success. Or is it posible to get in touch with the author of this circuit.

The other question is, Was this project ever built to prove that it works or was this just a theory design?

Thanks
Pieter

[audioguru]

Hi Pieter,
I didn't check the design nor your pcb for the maze of parts around IC3B. Maybe it is normal for it to give a repeating 1 second pulse without an input due to the high gain front-end amplifying its own noise. Maybe with a strong input signal it will be fine.

When you attach the power, D1 lights up and stays on because IC2A self-biases itself to mid-supply. It doesn't matter because D1 should follow the input pulses when the engine is running. If D1 doesn't blink when the engine is idling then maybe the coil isn't close enough to a spark plug wire.
Try swinging a magnet in front of the coil and the LED should blink.

I did a search of this site and didn't find comments about this project, so maybe you are the first person to build it. E-mail the author about it.
Last year I fixed his Plants Watering Watcher project here that was missing an important capacitor. I e-mailed him about it and he said it was designed a long time ago. It still has the error on his own web-site. ;D

[pieterw0]

Hi audioguru

I havn't thought of trying the project in this state. I will try the way you sugested.

I have gone to the RED FREE CURCUIT DESIGNS web page. At the bottom of the page there is buttons e-mail and questions. I have posted a few e-mails without any reply.

If this is the e-mail you are talking about then I won't even bother. As I said he doesn't even reply to the e-mails you send.

Is there perhaps any other Speed Alert curcuits available that you know of that works?
If so, could you direct me there.

Thanks again
Pieter

[audioguru]

Hi Pieter,
Many people have made a modern simple Speed Alert project with an LM2907 or LM2917 frequency to voltage converter IC. It is available in 8-pins and 14 pins packages, the 14-pins one has a built-in zener diode voltage regulator, their outputs can source or sink up to 100mA and one is made for breaker points and the other is made for a variable-reluctance (coil and magnet) sensor.
The product sheet with links to the datasheet and an application note is here:
http://www.national.com/pf/LM/LM2907.html

[pieterw0]

Hi Audioguru

Ok! I have some success. I had a look at the data sheets for IC1, IC2 and IC3. On the data sheet for IC 1, I noticed that pin 4 and 7 are not widely used in some of the app examples. I  disconnected pin 4 and “Walla”. It works.

The only drawback of this circuit is that it is effective at 30cm from a plug wire. Beyond this point it doesn’t work. I Have tried different coils with only little improvement.

The conclusion I came to, if I want to keep it “WIRELESS” I would have to split the project into a transmitter and a receiver. The transmitter transmitting the pulse frequency and the receiver receiving the frequency and converting it to volts in order to be able to adjust the required setting.

Now I had a look at the Gasoline Engine Tachometer IC  LM2917 that you refered me to and thought it has much less parts. The problem with this is that the IC already converts the frequency to volts, so I can’t use that in the transmitter

I am a hobbyist. I haven’t got a clue how to even begin to design an application.

What I would like for you or any one in the forum to help me with is;

Where do I start.
1) I need a configuration to pick up the pulses and transmit it to the receiver.
2) I need a configuration to receive the pulses. (This is the part where the frequency needs to be changed to volts (I THINK). Within this board I must have the ability to select a certain speed and an alarm to warn if the speed is exceeded.

If I have it correct. You select a certain volt and if the voltage exceed the set voltage the alarm sounds and the led flashes.

Thanks
Pieter

[audioguru]

Hi Pieter,
Pins 4 and 7 on a TL061 opamp are its power supply pins. They aren't shown on some app examples because it is assumed that they are connected. I don't see how your circuit can work without pin 4 grounded.

Most vehicle applications for a speed-limit alert use a shielded cable through the firewall to the sensor at the spark-plug wire. It would be difficult to build a good radio transmitter and even more difficult to make a radio receiver that didn't overload and activate the alert each time you drove near a radio or TV station.

You could make the LM2917 circuit and mount it at the engine. Its output could apply power to a purchased radio transmitter module. A matching purchased radio receiver module can activate the alert when it receives the carrier frequency from the transmitter. ;D

[pieterw0]

Hi Audioguru

It is fact. I agree with you. It is shown as hidden power pins, but what I did was to start cutting tracks. Remember I said that D1 and D5 with it's buzzer  would sound from beginning to end non stop. I have even moved the unit next to the spark plugs and wires and wouldn't change. I then disconnected pin 7 & and 4. The unit was then dead. I connected pin 4 again and there was nothing. Then I disconnected pin 4 again and connected pin 7 and all of a suden I got a reaction.

The reaction was that D1 responded to about 1.5 meter from the spark plugs. If I turn around away from the engine D1 does not light. When I turn back towards the running engine D1 starts to flash again.

D5 and buzzer on the other hand only responds about 30cm from the spark plugs. When I move the unit further than that 30cm it stops to sound. With this in mind. R11 was set to about 1/4 of it's adjusting ability. With the unit about 30cm away from the spark plugs nothing sounds. When I ref the engine to a certain RPM D5 and buzzer starts to sound. When I release the throttle on the carburetor D5 and buzzer stops to sound.

This tells me that the unit is now working, but not as it should.

If D1 picks up a frequency to about 1.5 meter then why does D5 and buzzer only works to about 30cm.

This means that If I have to reconnect pin 4 to equalize D1 and D5, something else must be wrong.

As I said. I know nothing about designing. I could build a curcuit. That is about it.
It would be nice if someone in the forum could build the unit and see if it works. If it works good. If it doesn't then the guru's can at least find the problem and post a proper curcuit with pc board that works. This is a nice project and I would hate to see that the money spend on the parts was wasted.

Thanks Again
Pieter

[audioguru]

Hi Pieter,
The instructions for the project say it can pick-up spark pulses from the engine when it is mounted in the cabin on the dashboard. I am amazed it is so sensitive. You probably must try it at many locations to find one that has the best pick-up from so far away. ;D

[pieterw0]

Hi Audioguru
Let's start from the beginning if you don't mind. One must accept that there is an inballance in the curcuit as it is.

If you look at the schematic. From L1 right through to IC 4098 and D1 and R9. This section picks up the signal to about 1.5 m.

Why does the second part not corespond with part 1. Surely the second part must warn from where ever the first part picks up the signal.

At the moment it is as if the second part is working on it's own. I have to move the unit closer to about 30cm from the spark plugs before it warns.

I am thinking logical here now. It seems as if the second part is ignoring the fist parts signal.

As I said. the second part must warn from where ever the first part picks up the signal.

IC3A is used as a frequency discriminator, its pin 6 going firmly high when speed limit (settled by R11) is reached. IC3B, the transistors and associate components provide timings for the signaling part, formed by LED D5 and piezo sounder BZ1. D3 introduces a small amount of hysteresis.

Any Ideas. Could one of the caps maybe be the cause of this? I don't know. Just asking.

Pieter

Ok this problem is also sorted out now.
I have disconnected R10. The unit sounds from the same distance as what D1 picks up the signal.

One final question!!!!!!!!!!!!!!!!!!!

How could i possibly increase the range of the pick up. What determine the range. Is it the size of L1 or is it also certain values of the resistors in conjunction with L1?

Thanks

[audioguru]

Hi Pieter,
To get more range, decrease the value of R1 and R2. Also, use an inductor with more turns and a lower resistance. Increase the value of R9 so that D1's current doesn't load-down the output of IC2.
I would try shorting C2 and removing R8. Then using a pot for R4 and R5 you could adjust the output DC voltage of IC1 to match the input switching threshold DC voltage of IC2. ;D

[prateeksikka]

hi audioguru!
sorry for the post at the wrong place.could u please have a look at the topic of MULTIMETER in chit chat section and help me out!i am in deep trouble ???

[pieterw0]

Hi Audioguru

I want to try a new concept. In fact, the one you suggested. This is the latest as you said. This IC converts frequency to volts. All in one. Hope I’m right!

So if you don’t mind lets start with the pick up and amp for now. I would like to keep it wireless. I have come to a point where the range on the old one was OK. I now need to incorporate L1 and IC 1 into this diagram. If I am correct. IC1 amplifies the signal. IC2A further amplifies the pulses and IC2B to IC2F inverters provide clean pulse squaring but, Do I need IC 2? As I see it LM2917 already gives out a clean voltage. I am not a designer so I really need some expert advice and guidance.

If possible could you draw me a schematic of how one would do this with the necessary resistors and caps.

I would really appreciate your input

Thanks
Pieter

[audioguru]

Hi Pieter,
1) You selected a tachometer circuit that gives a linear voltage output with the speed of the engine. It would need an external comparator and driver to switch on an alert device.
The circuit I posted uses the comparator part of the IC to "switch" on its driver transistor when the pre-set speed is reached, which I think is what you want.
2) You have selected the 8-pin version of the IC that needs an external zener diode.
The 14-pin version of the LM2917 has a zener diode built-in.
3) The 8-pin versions have one input grounded, requiring the preamp to have positive and negative supply voltages. The 14-pin versions have differential inputs so one input can be biased to the voltage at the output of a single-supply preamp.

So you need a 14-pin LM2917 IC, in the "speed-switch" circuit that I posted.

I don't think the IC1 preamp circuit of the other project has enough gain for your "long-distance" application. Therefore its IC2 circuit is also required. ;D   

[pieterw0]

Hi Audioguru

Yes it’s excellent. This is what  I had in mind. Just a few questions.

1) The old IC1 and IC2 will amplify the signal to keep it long range. R8, D1 will still indicate the best sensing  position of the unit. Is this correct?

2) Pin 3 of IC LM2917 with the trimmer will select the different cylinders. 4, 6 and 8. Is this correct?
Or do I use the trimmer on pin 3 to set the required speed?

The load is the warning part. Is this correct?

Thanks
Pieter

[Guest Alun]

Good idea audioguru, could you replace IC1 and IC2 with a dual op-amp?

[Dazza]

Hi all :),

pieterw0, you probably already thought of this or you may not want to go this way about it, but what kind of speedometer do you have, electronic or mechanical?

[audioguru]

Thanks, Alun. ;D
I think the 4 cascaded inverters will have a reasonable bandwidth and have much more gain over the bandwidth than an opamp. It is good to have the very low output impedance of the opamp as the 1st stage, to avoid positive feedback from the paralleled inverters output to the input of the 1st inverter.
Imagine how low-level the signal from the spark-plug cables would be when picked-up in the car's cabin. This circuit might even be able to pick-up a signal from another car beside you on the road! ;D

[pieterw0]

Hi Audioguru and guys.

Could you go back a few posts please! There is a few questions that I would like for you to answer, if it is not to much trouble.

To answer Dazza’s question.
I have a mechanical speedometer. This brings about a different topic. The application I want is a unit that if I preset it to 60mph then it must switch the buzzer and LED on at that point. So in other words all above 60mph this unit must moan until I reduce speed below 60mph. Once below 60mph the warnings must stop. This is actually all I need. The Speed limit alert circuit on the website doesn’t work so I’m looking at alternatives.
BUT
As far as I know the tachometer is the only way to go as far as wireless is concerned. Once you go the speedometer way you need a fixture like a shaft that you can count the number of revolutions per minute.
This will be to expensive.
I would rather settle for a small inexpensive way to warn me of over speeding. (Something I am guilty of many times)

Audioguru
You spoke about the 4 cascaded inverters. IC1 and IC2 is not that hot. Not to forget. IC3a also has some amplification. You must move the unit back and forth and sideways in the cabin to get a proper signal. The signal I found was basically next to the wind screen. (Not a good position) The LM2917 also has some amplification in the first of it’s three parts.
If you think that the 4 cascaded inverters discussed with Alum, will work better I would rather go for that.

Give me the schematic for a decent Speed alert with a buzzer and LED warning and I will build it.

Just for interest sake:
I have rebuilt the L1, IC1 and IC2 section again. If pin 4 of IC1 is connected D1 stays lit and doesn’t pick up a signal. Once disconnected D1 goes out. It starts flashing when a signal is detected.

Pieter

[Guest Alun]

Audioguru,
I think the TL082 will do, and if it's not good enough you could use the quad version TL084, I sure you could save an IC as three is far too many. ;D

[pieterw0]

Hi Audioguru and guys.

My humblest apologies to every one on the forum !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I found out by accident that with pin 4 on IC1 connected works.
The fact of the matter is that my computer is on the work bench. Having said this the magnetic pulses generated by the computer screen caused D1 to light. No matter in whatever position you turn R8 the led stayed lit. This was also the reason that the buzzer went beep on a per second basis. My computer hanged and I had to switch it off. Only when I did this I noticed that the led had gone dead. After restarting I moved away from the computer. The further away I moved the dimmer it got. So for about 2m + D1 goes out completely.
To give you an indication how strong the pulses is, it as if the LED gets full voltage. The brightest a LED can go.
I never realized that this was a factor. I am trying to kick myself in the butt but I can’t reach.
Sorry guys.
I am reconstructing the unit off all the damage I did to the tracks now so will let you know what happens.
I will also try the new design. Who knows. Maybe both could be posted with pc boards on the web site.

Pieter