Voltmeter

[Jony_BC]

Hi there guys. I was trying to make a voltmeter for my car but i wanted to try not spend any money. so i found five of this electronic gauge from a truck dashboard.
but i can´t find a way to controll-it I have tried diferent voltages, make it move but not the way i want it.

The truck that it was remove from its and Mercedes-Benz Actros(the first one) Also the same dashboard for Econic model.
It uses two 12 v batterys in series, and it charges until 28v

the maker of the dashboard is VDO and says this on the circuit board:
MANNESMANN VDO
1520.71.020.27 L2

If someone can give me some help. I will post the pictures of the gauge and circuit of dashboard(sorry for the low quality.

Thansk

 

[MPep]

I don't have the answer you seek, but we need more info. Truck make and model that the gauge has come from would help.

Remember many trucks are at 24V (28.8V) and cars are at, nominal 12V (battery terminal @ 14.4V).

 

[Jony_BC]

...

I there. thanks i will edit and put more information.

An i can find the circuit board of it, Just give 10 minutos and i will edit the post.

Thanks for the help

 

[Dippy]

Controlling this with PICAXE will be an interesting project.
Do you have any plans as to how PICAXE will be used?

 

[MartinM57]

IIRC these are very simple instruments that need pretty complex electronics to drive them - something like the needle moves according to the phase difference between the alternating currents passing separately through each coil...which probably means analogue circuitry rather than a digital/PICAXE solution.

I just can't rememeber where I read about them

 

[Jony_BC]

Hi there

Yap i´m sure its analog.
Dippy as soon as we figure out they are driven i think the best and maybe the only way is using PWM.

i´had already driven 0 to 7 volts from only one coil and get almost half way but if put 12 or 24 volts in the same coil it gets exaclty the same way in the end.

and it moves really slow. in the truck in their normal work their quite faster.

Nice was crank one open and let it work in the car. and read the values, But it will be hard to explain to the boss what i´m doing.

here are the picture off the circuit board.






Thanks

 

[boriz]

I take it that it’s open circuit between the two left and right terminals?

Looks to me like two solenoids back to back. Energise one and the needle moves left of centre. Energise the other and it moves right. Extent of deviation determined by relative currents.

If so, it could be used as a voltmeter in two ways.

First way. you ignore one coil and just control the current to the other. This would deflect the pointer only half of the full display though if you were using positive current only. Full range may be achieved by using an H-bridge.

Second way. You control the current to both coils separately. Balancing them, allowing full range deflection.

Both are possible using PWM. Both are quite efficient (centre position = nominal display = no current), though in terms of best efficiency I would probably favour the two coil method. Just because it uses only two transistors.

 

[Jony_BC]

...

thanks boriz

I´m not sure if i got your question right but.

I i measure from left pin to center pin i get 277 ohm, from right pin to center pin also 277, and from left to right get 500 ohms or so.

I already energise the left one making the center pin positive, And it got almost half way, I used a potenciometer that i had around the shop and energise 0 to 7 volts

But when i tried to put 12v just to see if i can just link it up right to battery to measure in end up exactly the same place. problaly it work just with 5v volts.

I just dont understand how i do that cause the center pin is comon and its positive. Do i have to turn off one coil when i energise the other? thats were the transistors get in? could you tell me more about that or give me some information to read about it, Or the name of this system, so i can gogglit I have already tried "electronic gause" and soo. but not very lucky.

Thanks for the greats replys

 

[hippy]

I was trying to make a voltmeter for my car but i wanted to try not spend any money.

Once you've worked out what it is, how to control it, built the electronics to do that and got it working reliably and accurately it may be far more expensive than buying a suitable meter which can simply be connected up.

I'd suggest taking a look in junk yards and eBay for something suitable.

 

[gengis]

The coils are in line with each other, so it looks like it is for 90 degrees of rotation? Autos have been known to use sin/cosine movements (for 270 degrees) but I'd expect them to be at right angles if that was the case.

I can't think of a sender that requires a tap, but maybe the tap provides a bias to provide voltage regulation (or movement regulation) in the event that the battery voltage is all over the place.

 

[Jony_BC]

....

Hi hippy. yap your right I was hoping that could only drive one coil just using and resistor and direct to the battery. But i will like to learn how they work. because i have more than then of them now and can get even more. is ashamed that they go to trash, and not use them in some future project.

Flooby i believe so, mostly because this gauge don´t even work as voltmeter in the truck. they are for speed, oi pressure, RPM and all of that.

thanks

 

[geoff07]

If you give up on these devices you can make a nice voltmeter with a compressed range (e.g. reading 10-15 volts, say, not 0-15) using a PICAXE 08M with analogue in and pwm out. You can use a digital filter to smooth the readings if they bounce around. All very simple and much higher resolution than a 0-15 meter. And almost no components except the chip and a few resistors plus some psu parts for the +5v. The meter in this case would be any milliameter taking less than say 10mA fsd.

 

[Jony_BC]

...

Yap another good idea. I just need to find out one that the needle dont move to much with the movement of the car. I had problems before with that a bump on the roud and there goes the needle.


I really was hoping to make this one with salvage parts, oh well if someone needs or wants one this electronic gauge that i have just say, we just need to find the best way to post-it The board also have 3 IC (TD62083AF) surface mount.

If find myself really needing one i just buy this one http://cgi.ebay.co.uk/Blue-LCD-Digital-Volt-Panel-Meter-Voltmeter-7-5V-20V-/300471754618?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item45f5831f7a#ht_2341wt_1139

But its always good to learn something in the process and if i can salvage some parts better.

I recently move for a new home but when i find all my stuff i will post a list of the salvage parts, a lot of motors I found one that lokes like its a tiny stepper motor.

Thanks for all your replys