Review on Tekpower TP4000ZC Auto Ranging DMM with USB Interface - PC Based Digital Multimeter, Similar to MS8220R, Computer Compatible by Tommie Lawson

I bought this for the RS232 function only. A phase of my residential air conditioner was failing and I wanted to check it. I have tried the complete software on Win 7 PC. It does not work. Knowing that finding an open source solution for Mac wouldn't be difficult, I decided to try it on my Mac Mini. Found QtDMM on mtoussaint.de (google). It didn't work on the first try. The COM port was not found. I used a serial to USB converter cable since my Mac (and indeed my Win 7 computer) didn't have serial ports. That's when I realized that I probably need a driver for the converter cable. It's not just a passive cable. It actually uses optical isolation. So you need a driver. The first attempt to try the Prolific.com.tw driver didn't work. Then the driver from Future Technology Devices (google it) did the trick. You will know the driver is working when you see the /dev/tty.usbserial device. After that I simply chose the multimeter in QtDMM that corresponds to the serial protocol for Tek, which is 8-N-1, 14-byte continuous binary. Digitech QM1538 fits. After that, sailing went smoothly. A $30 multimeter that you can use to record data is a bargain. 4 stars for this feature alone. I can't say anything about accuracy/accuracy etc. (yet). To update. After installing Win 7 serial to USB conversion drivers from Future Technology I was able to get the RS232 communication to work. It is set to COM3 and I was able to collect data using the software that came with it. Brilliant!