Need help with 2 ideas

[stuee]

Hi, well these are my car ideas, i have bit of electronic experience, but need help now,
1st im looking for a schematic for a ammeter on my car, it will be placed at the end of my 0awg cable in before my amps so i can see how many amps my system is drawing, i 3 X 7seg display will be fine and amperage is upto 100a. any ideas?

Also i have a schematic for a digital volume control http://www.aaroncake.net/circuits/volume.htm - but i want it for my car with a display so i can choose a chanel, ie rear, front, sub 1 or sub 2, then change the volume for what i select, also it has to remember, i know this circut forgets its setting when power off, bt it want it to remember too.

If any one chan help i would be most greatfull, schematics would be super
Thanks In advance
Stu

 

[audioguru2]

Stuee,
1) Ammeter: Meter manufacturers should have a current-shunt that you connect in series between the amplifier and battery. To allow for a voltage-drop of 0.1V at 100A, the shunt must be 0.001 ohms and be able to dissipate 10W. Then you connect a digital voltmeter having a full-scale sensitivity of 0.1V across the shunt. In order to keep the readings stable, use a peak-detector circuit ahead of the voltmeter. Our LED digital voltmeter project is here:
http://www.electronics-lab.com/projects/test/014/
Our voltmeter can be modified to give 0.1V full-scale.

2) Digital volume control with display, channel selection and memory. This sounds like it will be a complicated circuit, maybe another forum member has an idea for a manufactured system.

 

[GPG1]

It is possible to use the drop across your existing wiring to measure the current.
The way I have done it is to use a magnetic field sensor like this:
http://www.allegromicro.com/sf/0750/
I rolled my own using a sensor and a modfied rectangular ferrite core
salvaged from an old tv line drive transformer

The pot you have suggested remembers the last setting. How many channels do you need to control

 

[steven2]

hope this helps in any way

View attachment 35832

 

[steven2]

sorey about the clarity i just had these scanned by my brother. they look ok when you use the zoom thing to zoom in on the scanned image but when i upload it theres no zoom thing for others to zoom in on it to see it better

 

[ante1]

stuee,

It is not necessary to use a shunt to measure the current. Just use the heavy wire as a shunt and an adjustable amplifier (op-amp) to interface the meter. Borrow a clamp am-meter and calibrate when the setup is ready. You should avoid putting in shunts in this circuit if not absolutely necessary. Remember that the wire to the starter carry much more than 100A when cranking the engine. I haven

 

[stuee]

Thanks all for your input,
the idea was that i have a digi volt meter brought, but wanted to make it when i flick the switch it shows me the amperage so i can see how many amps my amps are sucking from the battery.