Good day all.

I hope you guys can help me, I am currently building a small Vehicle signal box to test some equipment,
basically it just need to give the basic signals out, like, brake, high beam, indicators wipers and most important Speed Signal, the box is basically done I just need to build a circuit to simulate a 12v speed signal. I originally build a small PWM circuit with 2 pots to change the on off times of a led out put, seems to work just fine but as soon as I hook it up to my system the signal is to low or slow that i cant get it up to 10 km/h.

I came across another type on the internet on a YouTube video that basically does not tell you a thing about it but does give you a diagram.

Can you maybe see if it will work, and as there is a 1:1 transformer in the circuit what should the specs be.

Also it only has to have 1 output and not four as shown on the diagram

I know I am asking alot but i have search every where i could and am out of ideas, this is a project for work and I sadly cant remember half the stuff about electronic I learned in School.

Thanks in advance.

 

That circuit has a couple of strange features but should work as a pulse generator. Not sure how closely the output resembles the signal from a real speed sensor. Can you post a link to the actual sensor you are trying to simulate?
Is it essential that the output signal ground should be isolated from the 12V ground?

 

Thanks for the reply.

Don't think is is essential that the output be grounded , as the whole system will be working of the same earth just as in a car, so the circuit and my equipment I'm testing will be grounded on the same common earth strap.
the signal should just simulate a standard transmission vehicle speed sensor.

here is a video I found to show you how it operates.

 

Maybe if the green LED is a flasher the output will be a low duty cycle blinking LEDs. Transformer might be a step down. If you describe what you want the LEDs to do, we can give you a better schematic.

 

Assuming your sensor is of this type, you don't need a 1:1 transformer if your instrumentation has a common ground. The simulator can be simpler than the one you posted.
The circuit below simulates a Hall type sensor with open-collector output. It covers a 30:1 frequency range which would typically be obtained with a wheel speed sensor producing four pulses per wheel rev. The two pots allow independently setting the mark and space durations of the pulses.

 

Mattred, your original circuit is wrong and will not work. The collector of the transistor should connect directly to 12V without the 1k resistor and the transistor's base does not need a resistor rated at 2W.

 

Thanks Guys, I will try this circuit in this week and get back to you, I am sure it will work, thanks Blocco a spirale but I never said the first circuit will work I just said I found it on the net and was wondering if it would work.

 

@alectravelyan sorry to sound like a real noob but what is the .asc file attached to your post, is that a file for the the simulator you are using?

 

@Alec_t sorry to sound like a real noob but what is the .asc file attached to your post, is that a file for the the simulator you are using?

 

Yes, the .asc file is for circuit simulation using LTspice (a free download from Linear Technology, as used by many members on this AAC site).

 

Thanks @Alec_t