I would like to try to hack a cheap harbor freight DMM, to use the case, display, and maybe the switch.
I'm trying to find specifics on the (unmarked) LCD display, its' 3" x 3/4". I found this somewhat idealized schematic here: http://www.hobby-hour.com/electronics/m830b-schematic-diagram.gif. The pin numbers 2-20 and 22-25 seem to match the way the PCB traces are laid if one assumes that pins 2-20 of the 7106 go to pins 2-20 on the LCD. But then I don't know what's up with LCD pins labeled 8, 12, 16 which seem to have to do with power.
The chip has a driver for each segment of the three full digits (3*7=21) plus the high-order digit which can be '1' or off, plus the minus sign: 23 pins altogether (2-20 and 22-25). The data sheet shows that the TEST pin (37) can be used to drive a decimal point (that's the transistor at the top).
I would guess that the two resistors to the right of the LCD, forming a voltage divider, are the contrast control.
If you want a cheap-ass seven-segment LCD you should get a calculator from the 1$ store. Many more digits and only $1!
I would guess that the two resistors to the right of the LCD, forming a voltage divider, are the contrast control.
Per the diagram it "seems" that pins 2-20 of the ic are going to pins 2-20 of the LCD. But the voltage divider uses LCD pins labeled 12 and 16. This is the conflict and puzzlement. Might require a datasheet to resolve. Who are some of the prominent mfg of LCD displays like this, I found Varitronix but couldn't match this display. Kinda hard to google because all the products that use LCDs come up
If you want a cheap-ass seven-segment LCD you should get a calculator from the 1$ store. Many more digits and only $1!
Great idea, thanks. But I kinda liked the form factor and rotary switch
I looked at hacking the harbor freight multimeter, but it appears to be an intergrated multimeter chip/display. One might consider using the rotary switch and resistor banks as an adapter for an arduino for converting voltages and resistances into something easy for the arduino to input.
zoomkat:
I looked at hacking the harbor freight multimeter, but it appears to be an intergrated multimeter chip/display. One might consider using the rotary switch and resistor banks as an adapter for an arduino for converting voltages and resistances into something easy for the arduino to input.
Now THERE'S a cool idea!
I'd LIKE to be able to make a "Multimeter Shield" that you could use to adapt to any electrical value the meter could measure.
Two approaches?? Use the resistance banks alone, Arduino Does Analog, or "decode the display" ?
I can buy these right out of the wholesaler in China...
I'd LIKE to be able to make a "Multimeter Shield" that you could use to adapt to any electrical value the meter could measure.
There are multimeters that have a serial output port that one could convert/adapt for communicating to a arduino board. Mostly just a RS-232 to TTL serial converter needed, like using a MAX232 chip.
