Simple Single Battery LPM

[brianpe]

I wanted to dust off my engineering skills and build my own LPM. Something simple with a pre-calibrated Ophir head and voltmeter. So really, all I built was a power supply. The supply runs off a single 9v battery. That is fed to a 7805 to provide stable power to the volt meter and to a DC-DC converter to upconvert to +/- 15v for the Ophir. I read on this forum of some folks having trouble with noise from the converter damaging the Ophir's amplifier, so I routed the output of the converter to a pair of 7812 / 7912 regulators and some reasonable filter capacitors. And I was careful to load the converter enough to ensure it stays stable, since the Ophir draws very little current.

And then I put it in a box that is entirely too big. But it looks nice.

Update: I've attached a zip containing the board, schematic and library files. You can use the free version of CadSoft's Eagle to generate gerbers for board manufacturing. If I could do it again I might mount the DVM connector on the opposite side of the board to give the boards more clearance. The DVM header has rather short pins for this type of mount.

Pictures:

Empty board, ready for stuffing.

Fully stuffed board.

I designed the board to piggy-back right onto the back of the volt meter.

Like I said: the case is way too big.

With the sensor connected it runs pretty close to zero. I find that this depends a bit on the ambient temperature. In the garage where it is colder it tends to be +1 or +2. At room temperature it runs at zero.

This seems to be pretty accurate. That's a 9mm diode driven at 2.1 amps.

Thanks for looking!

 

[HitShane]

Nice work What do you think the parts cost you total?

 

[ARG]

Looking good mate! I like the design.

You should put the gerbers out for that board or make a few of those and sell it, I know there are quite a few people with DIY Ophir heads that would want one.

 

[awillis2589]

Nice work!!

 

[brianpe]

I will update the post tonight with the gerbers and/or .brd file and schematics. Total cost wasn't terribly cheap: you could buy a Laserbee for less, I think. I spent about $100 on parts, $50 on board manufacture and about $150 on the head. The digital volt meter was the most costly part and I didn't shop around. If it was available on DigiKey I stopped looking.

 

[awillis2589]

No still cheaper than a laserbee. Well depending on which one. But personal I would take your setup over one of those. Nice work.

 

[ARG]

I will update the post tonight with the gerbers and/or .brd file and schematics. Total cost wasn't terribly cheap: you could buy a Laserbee for less, I think. I spent about $100 on parts, $50 on board manufacture and about $150 on the head. The digital volt meter was the most costly part and I didn't shop around. If it was available on DigiKey I stopped looking.

That's not to bad for a clean build like that

 

[IsaacT]

That is a sexy LPM, I really like the curly cord that looks like the telephone cords back when they had cords....sometimes I miss them....the cords, that is. And where did you find an Ophir head for 50 bucks?

Thanks,
Isaac

 

[ARG]

That is a sexy LPM, I really like the curly cord that looks like the telephone cords back when they had cords....sometimes I miss them....the cords, that is. And where did you find an Ophir head for 50 bucks?

Thanks,
Isaac

They used to sell for 40$ a few years ago.

Supply got dry, demand stayed the same, price went up

 

[awillis2589]

He said $150 for the head by the Way.

 

[IsaacT]

I meant to type 150 but I was on a sh*tty keyboard at school :/ That is still 50 bucks cheaper than any I can find currently.

 

[ARG]

I meant to type 150 but I was on a sh*tty keyboard at school :/ That is still 50 bucks cheaper than any I can find currently.

They are 180$-220$ now. I don't think you'll get any better than that.

 

[brianpe]

I got the head on ebay -- some company was selling them as surplus. I remember it was the only one for that price that didn't look like someone had run it over with a truck.

 

[brianpe]

That is a sexy LPM, I really like the curly cord that looks like the telephone cords back when they had cords....sometimes I miss them....the cords, that is. And where did you find an Ophir head for 50 bucks?

Thanks,
Isaac

Ha. I spent extra on the cord -- it is a phone cord. You can spend days surfing the cable offerings on DigiKey. After browsing for far too long I came upon this and decided it was the one. It plugs in with an RJ45 jack too. I was a bit worried because it isn't shielded but it doesn't seem like I'm getting any interference. I got the head on ebay for 150. Sounds like they're more now -- I guess I just got lucky.

 

[ARG]

Just saw the files, nice job on the design

 

[Tw15t3r]

Wow... that's a really compact and sleek setup!

I'm working on creating one myself, and I have a couple of questions.
- How much current does your voltmeter consume by itself?
- How much current does the OPHIR consume? (I heard it's 5mA, but want to just verify)
- How much current does the total setup consume (at your supply of 9V)?