Gaussmeter Kit Group-Buy

[Joe Gwinn]

Originally Posted by RedHouse

Easy Joe, I'd leave that for the experienced folks only, inexperienced experimentation with the input line to the PIC might ruin the PIC also. It's cheaper to get another A1302 than another PIC from Italy.

But how will they become experienced (=scarred for life)?

I recommend members build their probe (w/o the PIC installed) then install the PIC and test the unit. (static strap on of course)

That would work, and one can use the voltmeter on the sensor output and a magnet to determine if the sensor works.

Try not to touch or otherwise play with the sensor wiring (PIC input) as little as possible.

I think I'll add a pair of 1N4148 diodes wired such as to constrain the sensor-output input line to remain between 0 and 5 volts, at the very least for ESD protection. Will the PIC tolerate all voltages between zero and +5v at its pin 2 input? I assume it will, and that it has some built in protection diodes.

Hmm. How closely does the Allegro sensor output voltage approach the Gnd and Vcc rails over the magnetic field range? I'll have to check this.

[Joe Gwinn]

Originally Posted by David Schwab

I had the same thought. That way if you accidentally pull the plug, you remove the power before anything else.

I have to agree with RedHouse here - hot swapping sensors is likely to lead to tears, and stereo plugs are not a reliable way to sequence power.

[David Schwab]

Originally Posted by Joe Gwinn

I have to agree with RedHouse here - hot swapping sensors is likely to lead to tears, and stereo plugs are not a reliable way to sequence power.

I have no plans on hot swapping them. I was just saying that if the plug was accidentally pulled it would remove power from the sensor if the tip was used for (+). I would power down the unit before changing probes.

Ideally I wanted to find a connector like the one on my Behringer mixer that connects the power brick to the mixer. It has three pins and a screw collar to secure it.

But I think the 1/4" phone jack will work well if I don't find anything I like better.

[realtonecustompickup]

Originally Posted by David King

Are you testing Fender rod magnets or Gibson bar magnets? Those figure would be very weak for the former and about right for the latter.
Fender A2 .188 x .75" =700-900G
Fender A5 .188 x .75 =1050-1300G

never mind -I see you are looking at HB magnets.

I repair the pickups to more than 700.

But I never knew a gauss.

How levels gauss affect sound ?

low levels = warm ?

high levels = bright ?

thank you

[Joe Gwinn]

Originally Posted by David Schwab

I have no plans on hot swapping them. I was just saying that if the plug was accidentally pulled it would remove power from the sensor if the tip was used for (+). I would power down the unit before changing probes.

Many plug-jack combinations usually achieve this sequencing, but not all, and not always.

Ideally I wanted to find a connector like the one on my Behringer mixer that connects the power brick to the mixer. It has three pins and a screw collar to secure it.

Philmore distributes such connectors.

General: LKG Home Page

Multipin connectors: http://www.philmore-datak.com/mc/Page%2054.pdf

I think these may also be a kind of DIN connector. (DIN has many connector standards, not just the few kinds that are loosely called DIN connectors.)

But I think the 1/4" phone jack will work well if I don't find anything I like better.

The miniature phone plugs and jacks will work as well as 1/4-inch, and are mechanically more suitable.

[52 Bill]

In order to change the input calibration to probe #1 or #2, the meter has to be powered down anyway.

Radio Shack has a 4-pin, "CB Microphone" connector set that has a locking collar.

[David Schwab]

Originally Posted by 52 Bill

Radio Shack has a 4-pin, "CB Microphone" connector set that has a locking collar.

That's the kind of thing I was looking for. I even looked on their web site... I never thought about CB Microphone plugs.

[RedHouse]

Originally Posted by Joe Gwinn

But how will they become experienced (=scarred for life)?...

Well yes, there is that!

Originally Posted by Joe Gwinn

...I think I'll add a pair of 1N4148 diodes wired such as to constrain the sensor-output input line to remain between 0 and 5 volts, at the very least for ESD protection. ...

I have a similar plan, back-to-back Zeners (aka Clamping Diodes)

BTW, did you build yours yet Joe?

[Joe Gwinn]

Originally Posted by RedHouse

BTW, did you build yours yet Joe?

Partially. I have built all but the sensor probe assembly, but have not put the circuitry into the newly purchased box yet.

The only problem I had was self-inflicted - I didn't initially notice that the soldering iron temperature was set a bit low, so soldering was difficult at first.

As for back-to-back zeners, that may not work, as the PIC is rated for one schottky diode drop below Vdd to one drop above Vcc. I would use two schottky diodes from Vcc to Vd, with center to the PIC input, and a series resistor at the PIC input.

[RedHouse]

Originally Posted by Joe Gwinn

Partially. I have built all but the sensor probe assembly, but have not put the circuitry into the newly purchased box yet.

The only problem I had was self-inflicted - I didn't initially notice that the soldering iron temperature was set a bit low, so soldering was difficult at first.

As for back-to-back zeners, that may not work, as the PIC is rated for one schottky diode drop below Vdd to one drop above Vcc. I would use two schottky diodes from Vcc to Vd, with center to the PIC input, and a series resistor at the PIC input.

Good to hear Joe.

My only "problem" was also self-inflicted. When I hooked up my first A1302 sensor I was looking at the data sheet (page-3) instead of Elepro's diagram, and read the pin config for the LH package (SOT) instead of the UA package (3-pin SIP) which we have....Doh!

Anyway, check out page 45-48 of the PIC16F883 data sheet, shows back-to-back zeners protecting the I/O pins.

[David King]

Those look like regular diodes, not zeners.

[-Elepro-]

about esd protection and external zener read pag92 of datasheet.....

[LtKojak]

... today the kit arrived!

Thanks to the Italian Post Office today I'm officially the one who got it DEAD LAST! Do I get a trophy?

I'd like to thank Brad and all others that contributed to make this Kit-Group Buy possible.

Time to warm the solder iron up...

[spy]

[RedHouse]

Originally Posted by -Elepro-

about esd protection and external zener read pag92 of datasheet.....

Just as Joe described.

Originally Posted by David King

Those look like regular diodes, not zeners.

I think you're right, after zooming in I see all the horizontal lines have a little tail.

[Joe Gwinn]

Originally Posted by RedHouse

Anyway, check out page 45-48 of the PIC16F883 data sheet, shows back-to-back zeners protecting the I/O pins.

I think they are ordinary silicon diodes, not zeners, because the text makes no mention of zener action, which means that zener action is not intended (although all diodes can zener).

This is actually good news. A pair of external diodes, especially schottky diodes, should confer great protection, between their greater physical mass and the lower voltage drop of a schottky diode.

The pair of diodes conducts the overvoltage to either Vdd or Vcc rail. It can be useful to put a 15 volt zener diode across the +9 volt input terminals, to protect the filter capacitors and 7805 regulator et al.

[RedHouse]

Originally Posted by Joe Gwinn

I think they are ordinary silicon diodes, not zeners, because the text makes no mention of zener action, which means that zener action is not intended (although all diodes can zener).

This is actually good news. A pair of external diodes, especially schottky diodes, should confer great protection, between their greater physical mass and the lower voltage drop of a schottky diode.

The pair of diodes conducts the overvoltage to either Vdd or Vcc rail. It can be useful to put a 15 volt zener diode across the +9 volt input terminals, to protect the filter capacitors and 7805 regulator et al.

Do you recommend any particular Schottly?

[Joe Gwinn]

Originally Posted by RedHouse

Do you recommend any particular Schottly?

It isn't that critical, but ON Semi's MBR160 looks suitable, although I have not used it myself. This device is characterized as a low-drop rectifier diode.

http://www.onsemi.com/pub_link/Collateral/MBR150-D.PDF

Selection Criteria:

Breakdown Voltage: All such diodes are more than adequate.

Junction Capacitance: Not important in this application, given the capacitance already there.

Ability to absorb a big pulse: It's a rectifier, not a tiny small-signal diode. Rectifiers lead a hard life.

Reverse Leakage: This is the key issue in the gaussmeter. Too much leakage will affect gauss readings. I chose the MBR160 mainly on this issue.

[mickmutante]

Finally i received my kit today..!!! I just ensemble and it works great..!!!
This weekend I'm going to build a wooden case for it....

I have a question.... does the capacitor probe tip goes in parallel with the black (ground) and red cable (V+)..??

Again thanks to every one that participates in the group.!

[RedHouse]

Originally Posted by mickmutante

Finally i received my kit today..!!! I just ensemble and it works great..!!!
This weekend I'm going to build a wooden case for it....

I have a question.... does the capacitor probe tip goes in parallel with the black (ground) and red cable (V+)..??

Again thanks to every one that participates in the group.!

Yes Mick, cap goes across the power and ground leads on the probe.

This meter does work great, someday when I can get over to Italy I'm gonna buy Elepro a beer!.
(or whatever he's drinkin)

[LtKojak]

Originally Posted by RedHouse

Yes Mick, cap goes across the power and ground leads on the probe.

This meter does work great, someday when I can get over to Italy I'm gonna buy Elepro a beer!.
(or whatever he's drinkin)

Hey! I'm in Italy too, you know...? A mere 1.698Km from Elepro... no big deal if you fly a helicopter...

[-Elepro-]

Originally Posted by RedHouse

someday when I can get over to Italy I'm gonna buy Elepro a beer!.
(or whatever he's drinkin)

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

[David Schwab]

I'm not in Italy, but my mother's parent were from there, so I'll just have myself a beer for you guys!

This weeks beer is Hoegaarden.

[defaced]

Originally Posted by David Schwab

This weeks beer is Hoegaarden.

Superb choice.

[StarryNight]

Next time I'm in Chieti visiting my family. I'm definately buying you guys una birra fresca.
cin cin

[RedHouse]

Originally Posted by -Elepro-

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-]

Originally Posted by David Schwab

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]

Originally Posted by -Elepro-

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]

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]

Originally Posted by David Schwab

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]

Originally Posted by RedHouse

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]

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.