We have interfaced this SPL meter to a TP-Link MR3020 running OpenWrt OS. The SL-814 had a few jumpers added to enable it to (10 always stay on and (2) be powered from the 5V on the USB connector.
Circuit mods: 1. Short C3 - causes it to turn on automatically and stay on whenever power is applied. 2. jumper USB pin 4 across to 9V power trace (the fat one) 3. Jumper C12+ to u3 pins 2+3 shorting +9 to +5 (note there are TWO 5V regulators on the board, one for digital +5 and one for Analog +5, a good design practice isolating the two) 4. short R8 making "low battery" and associated not helpful auto power off go away
Cable mods 1. My SL-814 from amazon did not come with a cable 2. the "USB" port on the SL-814 is a USB port in physical form only. What they are doing is using a USB connector to output serial TTL I/O from the Atmel's UART. it is in no way, shape orm for USB and the claims on Amazon etc that it has USB are flat out false. 3. Use a PL2303 to TTL cable and a USB type B connector donor cable. 4. connect
i. black - black ii. red - red iii. green - white iv. white - green
End Result Plug into your PC, assuming you have PL2303 driver should show up as a COM port or /dev/ttyUSBx in the case of OpenWrt/Linux.