Power Pins

• VIN - this is the power pin. To power the board, provide 3V to 12VDC. There is an onboard regulator that will pin the input to the 555 and buffer to 5V max. That means that between 3V and 5V power, the signal peak will be at the same logic level as the power. Above 5V, the output will be pegged to 5V.
• GND - common ground for power and logic.

Signal Output

• SIG - this is the output signal from the 555 timer. It is a DC square wave, driven by a 74HC1G04 buffer so it can sink/source up to 12.5mA.

STEMMA JST PH

• STEMMA JST PH - 2mm pitch STEMMA JST port for use with 3-pin STEMMA JST PH cables. It has connections for:
  • GND - common ground for power and data. It is the black wire on the JST PH cable.
  • VIN - power input for the 555 timer. It is the red wire on the JST PH cable. 
  • SIG - signal output from the 555 timer. It is the white wire on the JST PH cable.

Range Selection Switch

On the top right of the board is a slide switch labeled 250 Hz and 25 KHz on the board silk. This switch selects between two 'ranges' for the 555 timer output: approximately 1.4~25 KHz or 1.4~250 Hz.

Frequency Adjustment Trimmer Pot

At the end of the board, opposite the JST PH port, is a trimmer pot. It is labeled Freq. Adjust on the board silk. This pot adjusts the actual frequency output from the 555 timer between the value range that you select with the selection switch.

Signal LED and Jumper

• Signal LED - to the left of the JST PH connector is the signal LED, labeled Sig. It is the red LED. It will light up when a signal is output from the 555 timer.
• LED jumper - in the center of the back of the board is a jumper for the signal LED. It is labeled Sig on the board silk. If you want to disable the signal LED, cut the trace on this jumper.

Power LED and Jumper

• Power LED - to the right of the JST PH connector is the power LED, labeled ON. It is the green LED.
• LED jumper - in the center of the back of the board is a jumper for the power LED. It is labeled On on the board silk. If you want to disable the power LED, cut the trace on this jumper.