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digital ammeter 7-seg LED display

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scholesy

New Member
Hi all,
I'm after a circuit (easy!) that I can build for my car to measure current. I have a 7107 A-D, and wondering if anyone has a circuit diagram I could use? I'd like to use single-digit 7-segs.

Alternatively, if you have another version that uses multi-plexing 7-seg displays, that would be good. I have 2, dual-7-segs I could use.

I did a search but couldn't seem to find anything.

thanks
:)
 

DirtyLude

Well-Known Member
Will that current sense circuit work for a regular microcontroller with an ADC as well? I'd like to measure current in a car application as well, and I'd like to use a microcontroller.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
DirtyLude said:
Will that current sense circuit work for a regular microcontroller with an ADC as well? I'd like to measure current in a car application as well, and I'd like to use a microcontroller.
Yes, it works just the same, but you have to be careful with the grounding arrangements - the circuit shown uses a totally seperate power supply to that of the circuit being measured. You should preferably do the same with a microcontroller, otherwise you need to arrange the circuit for it not to matter (which may not be easy!).
 

Johnson777717

New Member
- the circuit shown uses a totally seperate power supply to that of the circuit being measured.
very good point. I realise that I should have pointed that out. Thank you. :)

Also, the resistor is 5 watt, because 5 watt resistors are easier to find. A 2-3 watt resistor would work here just the same.
 

scholesy

New Member
thanks everyone esp. Johnson777717.

I suspect car currents would be a lot higher than 2A (judging from my fusebox at any rate). What component values would I use / how would I get the 7107 to handle higher loads? I'm guessing up to 20A would be ok to display.

cheers :)
 

ljcox

Well-Known Member
See page 53 of the September 2003 the Australian magazine "Silicon Chip"

The article is entitled "Current clamp adapter for multimeters" it uses a Hall Effect device inside a clamp that is placed over the wire to be measured (ie. no electrical connection is necessary) and they claim it can be used for up to 150 Amp for DC and 630 Amp for AC (with a -3dB point at 20kHz)

The output is connected to a normal digital multimeter.
 

scholesy

New Member
Hi Len,
I don't have access to Sep03 of that mag. I have Dec03 (I think) that has a digital voltmeter.

My memory's a bit murky; but I remember reading somewhere that a 7107, a DickSMith q2230 panel meter, and a handful of components would make an ammeter. Wish I could remember where.

150A??!! Hell. Mind you, I s'pose ignition currents would run pretty high. Maybe I'd run the scale at 199.9 rather than 19.99!!
 

Nigel Goodwin

Super Moderator
Most Helpful Member
scholesy said:
Hi Len,
I don't have access to Sep03 of that mag. I have Dec03 (I think) that has a digital voltmeter.

My memory's a bit murky; but I remember reading somewhere that a 7107, a DickSMith q2230 panel meter, and a handful of components would make an ammeter. Wish I could remember where.

150A??!! Hell. Mind you, I s'pose ignition currents would run pretty high. Maybe I'd run the scale at 199.9 rather than 19.99!!
Ignition current should be relatively low, but starter motor currents are massive - 150A would be fairly usual!. If you're wanting to measure the total battery current, an easy way, without modifying the car in any way, is to use an opamp as a differential amplifier to measure the voltage drop across the earth lead from the battery to chassis.
 

ljcox

Well-Known Member
scholesy said:
Hi Len,
I don't have access to Sep03 of that mag. I have Dec03 (I think) that has a digital voltmeter.

My memory's a bit murky; but I remember reading somewhere that a 7107, a DickSMith q2230 panel meter, and a handful of components would make an ammeter. Wish I could remember where.

150A??!! Hell. Mind you, I s'pose ignition currents would run pretty high. Maybe I'd run the scale at 199.9 rather than 19.99!!
Yes, you could do it with a panel meter, but this would require you to break the circuit and inset a shunt. Whereas, the SC design simply clamps around the cable.

Len
 

scholesy

New Member
Hi Len,
I tried to email you to say yes; a copy of the Dec03 article would be great, but the mail bounced... no idea why.

I like the concept of disturbing the car's electrics as little as possible... and placing my panel meter in series to measure current would not be my favourite option, esp. if there is a more cunning way of doing it.

cheers :)
 
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