Basic Pulse generation help

[john2k]

Hello,

What voltage did you get on pin 20?
Is it about the supply voltage?
It can be there is a pull-up resistor inside the unit.

Bertus

I got around 10V on pin 20. It's not the same as supply voltage as supply is 12V to 13V. When I measure voltage on pin 19 which is supposed to be speed signal output, I get a much lower voltage reading I cant remember exactly how much i think it was something like 3 or 4 volts. If i connect a LED to pin 19 it gets a very litte bit of power and u can just about see a little bit of the LED. But on pin 20 the LED powers up fully. The LED i'm testing with has a inline resistor built in to be able to handle 12v

 

[bertus]

Hello,

What kind of meter did you use?
A DMM (Digital Multi Meter) or an analog one ?

Bertus

 

[john2k]

Hello,

What kind of meter did you use?
A DMM (Digital Multi Meter) or an analog one ?

Bertus

A DMM. One of those yellow ones.

 

[john2k]

Keep your resistor and LED connected to pin 20 but disconnect the other end from ground and connect it to the collector of a 2N2222 transistor. Connect the emitter of the transistor to ground and the base to a 1kohm resistor - join the other end of the resistor to the pulse gen output. Job done. The LED should pulse showing the thing is working - if not, remove the LED and your resistor and connect the collector of the 2N2222 directly to pin 20. I'm trying to avoid shorting pin 20 to ground by drawing too much current from it. The 2N2222 is taking the place of the hall effect sensor.

Silly me, i didn't read your reply properly. I think now that i've read through it properly it makes a lot of sense. So from pin 20 to my LED red wire (with inline resistor). From LED black wire to the collector of the 2N2222. The emitter of the transistor to the common ground (body of the cluster) The base (middle pin) of the transistor to a 1k ohm resistor and then to the output of the pulse generator. I think that's right?

 

[bertus]

Hello,

You could try it the way you describe.
It can be that the signal goes not low enough, but to the test.

Bertus

 

[john2k]

Hello,

You could try it the way you describe.
It can be that the signal goes not low enough, but to the test.

Bertus

I've ordered some 2N2222 transistors, hopefully it will arrive tomorrow for me to test out

 

[bertus]

Hello,

Do you have any other transistors available?
It looks like any small signal transistor can be used.

Bertus

 

[majoco]

Ah - I didn't know that your LED had an in-built resistor! You had the LED from pin 20 to ground to indicate that there was voltage at pin 20 - so just disconnect the ground side and join it to the collector of the transistor.

Any NPN low power transistor will do, I just said a 2N2222 as they are very common, 2N3904 will do too. You may like to buy some red LED's at the same time as the resistor that is already built in to your LED may be too high if there is already a resistor in the cluster in series before pin 20. What we are trying to do is to pull the 10volts at pin 20 down to near zero by turning on the transistor with the pulses from the square wave generator - if your LED doesn't indicate then remove it and put an ordinary red LED in it's place - no resistor.

Let us know how you get on - I don't think you're going to blow anything up! What power supply are you using to power the instrument cluster - hopefully not a car battery! Don't worry about pin 19, I don't think that's going to do anything useful until you get the wheel speed working - it may be an output to give the wheel speed to some other computer - engine and gearbox computers need lots of signals for best performance and the ABS wants to know too but I think that's in the cluster.

 

[john2k]

Ah - I didn't know that your LED had an in-built resistor! You had the LED from pin 20 to ground to indicate that there was voltage at pin 20 - so just disconnect the ground side and join it to the collector of the transistor.

Any NPN low power transistor will do, I just said a 2N2222 as they are very common, 2N3904 will do too. You may like to buy some red LED's at the same time as the resistor that is already built in to your LED may be too high if there is already a resistor in the cluster in series before pin 20. What we are trying to do is to pull the 10volts at pin 20 down to near zero by turning on the transistor with the pulses from the square wave generator - if your LED doesn't indicate then remove it and put an ordinary red LED in it's place - no resistor.

Let us know how you get on - I don't think you're going to blow anything up! What power supply are you using to power the instrument cluster - hopefully not a car battery! Don't worry about pin 19, I don't think that's going to do anything useful until you get the wheel speed working - it may be an output to give the wheel speed to some other computer - engine and gearbox computers need lots of signals for best performance and the ABS wants to know too but I think that's in the cluster.

Hopefully i'll get delivery of the 2N2222's tomorrow so I can test it out. I dont think I have any red LED's laying around and none without built-in resistors. I could potentially remove a red LED from some old things that may be laying around.

I'm powering it from a cig light socket using the following indoor AC to 12v DC unit: https://www.halfords.com/camping-le...lfords-coolbox-mains-to-12v-accessory-adaptor

 

[john2k]

The base on the 2N2222's are always the middle pin right? Then how do you tell which is collector and which is emitter?

 

[majoco]

You can't make a general statement like that! If the 2N2222 comes in a metal can it will have a little tab on the can near one of the pins - that will be the emitter, the base in the middle and then the collector which may or may not be connected to the metal can.

 

[john2k]

So I received the 2N2222 and will try it out later today. The drawing supplied by the supplier is below. So based on this. am I correct in understanding that the middle pin is base. With the transistor with the flat side facing me the left pin is emitter and the right is collector. So with the flat bit down the emitter and collector will be reversed

 

[Martaine2005]

That is correct. Flat side facing you and legs pointing at the floor.
Flat side down? Would depend on leg direction.
Flat side down and legs pointing to the floor, then yes.

Martin

 

[john2k]

Let us know how you get on - I don't think you're going to blow anything up! What power supply are you using to power the instrument cluster - hopefully not a car battery! Don't worry about pin 19, I don't think that's going to do anything useful until you get the wheel speed working - it may be an output to give the wheel speed to some other computer - engine and gearbox computers need lots of signals for best performance and the ABS wants to know too but I think that's in the cluster.

So I tried this interface using the 2N2222 and the square pulse wave generator. The square wave generator has 4 jumpers low to high. I tried from the low to high and played around with adjusting the potentiometer clockwise and anti-clockwise but the cluster just wasnt responding with any speed being recognised. The LED i placed blinks at different speeds depending on the jumper setting and the potentiometer adjustments.

 

[john2k]

I also tried putting a led without the resistor. Led blinks nicely and the rate of blink is adjustable with the potentiometer. I also tried directly from the collector leg to pin 20 but still no speed being detected. Any ideas?

 

[bertus]

Hello,

The speed that will be detected is likely so high that you will not see the led blink.
Adjust the speed much higher and see if there ia any change.

Bertus

 

[john2k]

Hello,

The speed that will be detected is likely so high that you will not see the led blink.
Adjust the speed much higher and see if there ia any change.

Bertus

There are 4 jumpers on the pulse generator, and the datasheet says:

The output frequency is continuously adjustable using the onboard jumpers and potentiometers. Jumper settings are:
1Hz ~ 50Hz
50Hz ~ 1kHz
1KHz ~ 10kHz
10kHz ~ 200kHz
The output duty cycle can fine-tuned using the onboard potentiometers. Duty cycle and frequency are not separately adjustable; adjusting the duty cycle will change the frequency


The output frequency and duty cycle are adjusted using the following variables:

Period T = 0.7 (RA +2 RB) C
RA, RB are 0-10K Ohm adjustable potentiometers
1Hz ~ 50Hz: C = 0.001UF
50Hz ~ 1kHz: C = 0.1UF
1KHz ~ 10kHz: C = 1UF
10kHz ~ 200kHz: C = 100UF

I tried going from lowest to highest jumper. When I put highest jumper, the led is solid but no speed detected on cluster.

 

[bertus]

Hello,

Wich range did you test?
I would try range 2 : 50 Hz - 1 kHz

Bertus

 

[john2k]

Hello,

Wich range did you test?
I would try range 2 : 50 Hz - 1 kHz

Bertus

I tested range 2 again now. No difference. There are two screws to adjust. When I screw the top one clockwise the board starts getting a bit hot

 

[bertus]

Hello,

Wich of the screws ia getting a bit hot?



That shoud not happen, unless it is a bad design.

Bertus