DIY Thermal LPM for under $50

[HIMNL9]

Uh, i hope i have NOT contributed to start a war, with my posts, cause that was NOt my intention at all .....

 

[lasersbee]

No HIMNL9... don't worry...:crackup:

You stated facts and ideas that make perfect sense...

There is no war or fighting or arguments here...
I just needed to respond to goninanbl00d's questions...:beer:


Jerry

You can contact us at any time on our Website: J.BAUER Electronics

 

[goninanbl00d]

I asked a legitimate question in regard to what you said.

If that's the way you want to be, then so be it.

Each to their own.

 

[lasersbee]

I gave you legitimate answers... in regard to your questions...
I still don't understand your reference to Nospin...:thinking:


Jerry

You can contact us at any time on our Website: J.BAUER Electronics

 

[goninanbl00d]

To answer your snotty questions as you posed them I'll
go through them as indicated by color above...

Was that really necessary?

I was just pointing out that you were suggesting something that was the exact opposite of what you did.

As for Nospin, I'm referring to the last time you flipped out when I asked about your LPMs. You'd really expect me to know about someone and sort through pages of sales threads to find him? Perhaps if he made himself known more, maybe.

 

[badger1666]

anyone got the circuit diagram for this project that was in post 1
its dissapeared now

thanks

 

[jib77]

anyone got the circuit diagram for this project that was in post 1
its dissapeared now

thanks

Here you go:

I still have plenty of these PCBs available(no parts installed):

 

[badger1666]

thanks jib77 thats a great help
hoping to get this project working in the week
as soon as my volt meter gets here,but may well use dmm for now

 

[badger1666]

Re: DIY Thermal LPM for under $50 help

hi all
need a little help please
finished my meter works great except i cant zero it properly
it sits at -5 with the pot at full turn, if i turn the pot it just goes
more into the minus , did i goof somthing up ??
note if i make the heat sink colder than ambiant temp it goes innto the plus and i can zero it

hope someone can help

thanks

 

[badger1666]

sorted

dont worry sorted it
read through the whole thread and found that the meter need to be on a different battery to the amp that fixed the problem , spot on zero now

 

[lazeerer]

Great.

Post some Pictures if you can.

 

[Xplorer877]

Re: sorted

dont worry sorted it
read through the whole thread and found that the meter need to be on a different battery to the amp that fixed the problem , spot on zero now

Yeah, thats what I had to do. Weird huh?
Congrats on getting it to work. :wave:

-Tony

 

[HIMNL9]

Some millivoltmeter modules don't allow the negative input pin connected to the ground pin of the power supply of the module itself, it's a limitation of the reading IC and cannot be worked around (and, trust me, i've tried almost anything, about it ) ..... the only working solution is to use a little DC-DC converter for power up the head circuit, so the two grounds are galvanically insulated.

 

[badger1666]

Great.

Post some Pictures if you can.

sorry for late reply to much work no time to play
i said finished , but ment finshed as in working but not complete
will post pics as soon as i get it done over xmas
but i got to say this was an excellent project
i am well happy with it, just need to calibrate it against another
meter

MERRY XMAS TO ALL

 

[badger1666]

Some millivoltmeter modules don't allow the negative input pin connected to the ground pin of the power supply of the module itself, it's a limitation of the reading IC and cannot be worked around (and, trust me, i've tried almost anything, about it ) ..... the only working solution is to use a little DC-DC converter for power up the head circuit, so the two grounds are galvanically insulated.

would not using a diode on the ground fix the problem ??
or is that not worth me trying

 

[HIMNL9]

would not using a diode on the ground fix the problem ??
or is that not worth me trying

Not at all, sorry ..... i've tried diodes, resistors, resistors network for get a "virtual ground", and so on ..... it just go offscale with nothing connected to input if the difference is low enough for let you read, and don't read at all if the difference is big enough for not drive the reading offscale .....

The only way i got for solve the problem was to use a mini DC-DC converter, and cause they can be found only with 5 and 12V input, here, and the module needs 9V of power supply, i used an LM1117 for get the 5 from the 9, then used it for feed the converter.

It's not a matter of the value and component that you can use for separate the ground, is an issue of the internal circuitry of all the millivoltmeters that uses that Intersil family chips ..... those chips, simply, cannot work if the -in is connected to GND.

Anyway, now there are more "moderns" chips that can read also with the two grounds connected together, just you need to test what module you get ..... it's easy, anyway, cause if you power it up with a 9V battery (and it correctly shows 0, or random ripple), and then you connect the -Vin to gnd, the old ones immediately jump offscale, when the new ones just continue to work as nothing happened ..... indicatively, if they have a big standard chip marked "71xx", usually 7106 (LCD) or 7107 (LED), they are the old types ..... same if they have a rectangular "resinated chip" (an oval blob of black resin that cover the bare silicon chip), or a quad pack chip, with few SMD components, a brown or blue capacitor marked "104" (100nF) and a trimmer marked "102" (1Kohm) on the back, also in this case 99,9% is the old type ..... if instead they have no chip, or a DIL SMD chip, and a small clock-type quartz, on the back, there's a good possibility that is a new type .....