Gaussmeter Kit Group-Buy

[RedHouse]

beerS .... perfect for me.... or I could come in Sammamish if you find BIRRA MESSINA there...

We don't have that, but we have plenty of local brewski's to choose from. This area is a micro-brewery haven.

[David Schwab]

I got my other sensor today... so it's time to finish the meter!

[-Elepro-]

I got my other sensor today... so it's time to finish the meter!

but, the ad22151?
i have not found one yet.....
would you try that i described in post#363?

you can test it with voltmeter....

[David Schwab]

but, the ad22151?
i have not found one yet.....
would you try that i described in post#363?

you can test it with voltmeter....

That's how I was going to do it. I will not have time to get to it until the weekend...

[David Schwab]

Almost finished!

So I worked on my case last night... got the holes cut and drilled, and assembled the meter inside. I swapped where I was going to put the power and backlight switches and redid my panel graphic. I used a thin sheet of clear plastic I had saved from some packaging... I think it was a new cordless phone. So I put that over the front and the switches and buttons hold it in place.

I haven't worked on my probes yet... I'll pick up the connectors today. I installed some right angle header pins and plug so I can wire that up and then plug it into the board.

Can't wait to power it up!

[mickmutante]

Nice..!!

[spy]

Great job! Awesome!

[RedHouse]

So I worked on my case last night... got the holes cut and drilled, and assembled the meter inside. I swapped where I was going to put the power and backlight switches and redid my panel graphic. I used a thin sheet of clear plastic I had saved from some packaging... I think it was a new cordless phone. So I put that over the front and the switches and buttons hold it in place.

I haven't worked on my probes yet... I'll pick up the connectors today. I installed some right angle header pins and plug so I can wire that up and then plug it into the board.

Can't wait to power it up!

Tell again how you made the label, is it a vinyl sticker or what?
(and great job BTW)

[David Schwab]

Tell again how you made the label, is it a vinyl sticker or what?
(and great job BTW)

Thanks. It was supposed to be something like a vinyl sticker... but I did it really low tech. That's what happens when you decide to make something at 10PM! I printed it on plain paper on my inkjet. I cut the various openings with a razor blade. Then I stuck it down with double stick tape.

Then I cut a piece of clear plastic that I salvaged from the packaging for a phone, and marked and drilled the corresponding holes. I placed it on top of the paper label and then mounted the switches.

Because I had a printed black outline around the LCD window, I was able to cut into that, which hides my not very straight opening in the plastic box!

[Joe Gwinn]

Gaussmeter built

I finished building the gaussmeter today. It works as expected.

I didn't quite follow the instructions. I left the sensor flat (not perpendicular to the cable), so I could slip it between strings and pickup, or put it into a constant-field calibrator. In use, I push the sensor against the pole piece with my finger. The sensor is on the far end of an 18" length of shielded twisted pair that I had in stock (for ~40 years). I did mount the 100 nF capacitor near the sensor.

The only interesting trick was that at the sensor end, after I soldered the various connections, I wrapped them with plumbers' teflon tape before fixing everything together with heat shrink tubing. The tape, which is inside the heat shrink tubes, will not melt. The sensor leads are also insulated with very thin teflon tubing, which won't melt during soldering or heat shrinking.

[mkat]

I finished building the gaussmeter today. It works as expected.

I didn't quite follow the instructions. I left the sensor flat (not perpendicular to the cable), so I could slip it between strings and pickup, or put it into a constant-field calibrator. In use, I push the sensor against the pole piece with my finger. The sensor is on the far end of an 18" length of shielded twisted pair that I had in stock (for ~40 years). I did mount the 100 nF capacitor near the sensor.

The only interesting trick was that at the sensor end, after I soldered the various connections, I wrapped them with plumbers' teflon tape before fixing everything together with heat shrink tubing. The tape, which is inside the heat shrink tubes, will not melt. The sensor leads are also insulated with very thin teflon tubing, which won't melt during soldering or heat shrinking.

Some good ideas there Joe. Did you end up using the diodes?

[spy]

I haven't worked on my probes yet... I'll pick up the connectors today. I installed some right angle header pins and plug so I can wire that up and then plug it into the board.

Are you planning to use a CB microphone plug or you changed your mind?

[Joe Gwinn]

Did you end up using the diodes?

No, because I hardwired the sensor to the gaussmeter. Both Allegro sensor and PIC have ESD protection diodes, and the shield braid of the cable is bare, so there will not be a voltage between user and gaussmeter.

I have a simple gaussmeter (Here) using an Allegro sensor and built on a piece of vectorboard, with no case or shielding whatsoever, and have had no problem.

I may add 1N4148 diodes nonetheless, from an abundance of caution and lack of experience with PIC chips. Although I would expect anything at the jellybean price-volume point of a PIC chip not to be too fragile.

If I were to implement the plug-and-jack design, I would add the diodes, if only to try to protect against whatever else might be plugged in by mistake.


When I do worry about ESD, particularly where there are very sensitive inputs, I design the protection in from the start, as it can be hard to add the protection later without degrading circuit performance. These are one-off projects, so the cost of parts is almost irrelevant.

Returning to the Gaussmeter, if I were really worried, I would have cut the trace between sensor output solderpad and the PIC input pad and inserted a series resistor to limit the ESD surge current. I have not done the work to figure out how large this resistor can be without unduly affecting measurement accuracy, but even a 10 or 100 ohm resistor can confer significant protection.

[David Schwab]

Are you planning to use a CB microphone plug or you changed your mind?

Probably. I'm going to go see if the local RS has them and then see what they look like.

[mkat]

I made a couple of leads for the probe, still haven't made the probe yet. One with a microphone connector and another one straight to the connector on the board. The shop only had a 5 pin unfortunately. Still undecided which I'll go with. Are these the microphone connectors you were thinking of?