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Want to build one? (part one, hardware)

A project log for Micro progmeter

Volt- and ohmmeter plus calculator on 25x25mm PCB

jaromir.sukubajaromir.sukuba 12/22/2015 at 10:470 Comments

PCB and components

Order PCB from your favorite supplies. You have Eagle PCB design files (to be opened in version 6 or higher) available here or gerber manufacturing data (generated by iteadstudio CAM file) available here.

Before the PCB arrives, you have plenty of time to order components according to this BOM. Passive components are jelly-bean parts and should be available anywhere, I bought them mostly at TME. Most of the resistors are 0603 parts, but some are 0805 sized - all those are in "sensitive" places, where absolute accuracy and temperature coefficient plays role, and better resistors make slightly better progmeter. I used 0,1% 25ppm parts for 6K8 and 470k from TME, and 10M and 1M from Mouser.

I bought PIC18LF1829 at Mouser, but it is available at Digi-key or elsewhere, as well as ADS1120 here and here. Analog switch NC7SB3157 is from TME, but available at Mouser too. TC1015 is cheap at TME, but Mouser keeps them too. The same goes for MCP1702 and second source. MCP73831 is etting jelly-bean part, like here and here and elsewhere.

Battery connector is type MX-53047-021, available at TME as usual, but Mouser is OK too. 2mm banana plugs are good at TME, but Mouser keeps similar one and this one. I have to admit the ones from Mouser feel cheaper, though it is actually more expensive.

BSS214 could be substituted to any low Vgs threshold NFET, IRLML6302 is here just generic low Vgs threshold PFET, BSS84 is available here and here.

Display is generic 0,49" OLED with 64x32 pixels resolution, available at aliexpress, as well as battery. Joystick is from TME, but is seems to be the same as from sparkfun.

Enclosure

Turn on your favorite 3D printer and while hotend and heatbed is heating up, download STL files for enclosure or play around with source files for Freecad. Notice I'm poor 3D designer, so professionals may be amused.

I printed this one of PLA.

Probes

DMM without probes is not of much use, so here you go. Buy one of those and those (or any other 2mm banana plug), pieces of 0,75mm square cross-section wire, the other end may be of your desire. I used old 4mm banana plugs from junkbox, plus antique 4mm alligator clips and I bought also those test probes too.

So now, hardware is prepared, let's proceed to compiling sources and calibration.

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