If you read about Hall effect sensors — the usual way to detect and measure magnetic fields these days — it sounds deceptively simple. There’s a metal plate with current flowing across it in one direction, and sensors at right angles to the current flow. Can it really be that simple? According to a recent article in Elektor, [Burkhard Kainka] says yes.
The circuit uses a dual op amp with very high gain, which is necessary because the Hall voltage with 1 A through a 35 micron copper layer (the thickness on 1 oz copper boards) is on the order of 1.5 microvolts per Tesla. Of course, when dealing with tiny voltages like that, noise can be a problem, and you’ll need to zero the amplifier circuit before each use.
The metal surface? A piece of blank PCB. Copper isn’t the best material for a Hall sensor, but it is readily available, and it does work. Of course, moving the magnet can cause changes, and the whole thing is temperature sensitive. You wouldn’t want to use this setup for a precision measurement. But for an experimental look at the Hall effect, it is a great project.
Today, these sensors usually come in a package. If you want to know more about the Hall effect, including who Edwin Hall was, we can help with that, too.
If the magnet is fixed, the output is proportional to current. This leads to a non-resistive (or extremely low resistive) current sensor, and these are also available in small packages.
Such as this one (randomly chosen):
https://www.ti.com/lit/ds/symlink/tmcs1108.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts=1766520069309
This particular one is also galvanically isolated.
Pity there’s no link to the Elector article. I was trying to suss out the circuit, but the image is cut off top and bottom. The top line goes straight across – I think – but it would be nice to see the original.
Looks like the battery and resistor dividers provide a +/- supply, the first op amp is a 6666 x inverting voltage amplifier (with offset null adjustment), and the 2nd op amp is apparently (?) a grounded voltage follower.
I don’t know why a 2nd amplifier is needed, maybe it supplies current to drive the voltmeter, or maybe it’s just not needed. It’s not explained in the article.
Can anyone shed light on this?
The article, since it isn’t in the blog post:
https://www.elektormagazine.com/news/circuit-diy-experimental-hall-sensor
Thank you. :)