Arduino based camera trigger circuit

Posted on Feb 6, 2014

The heart of the circuit consists of the Arduino microprocessor which is indicated by the header pins on the left of the circuit schematic shown on the right (click to open in new window). Two of the analog inputs (0 and 1) are connected to the emitter sides of TEMT6000 ambient light sensors (Vishay Semiconductors, Shelton, CT), which act as laser targets. When light shines on these sensors, current runs from collector to emitter, so that the analog inputs are close to 5 V. In darkness, no current flows across the transistors, and the 10 KOhm resistors pull the inputs to ground. In a realistic situation, when an object blocks the laser beam impinging upon a sensor, the voltage will be somewhere in between 0 and 5 V, which gets encoded as a value between 0 and 1023 by the 10-bit analog converter. (The alignment routine described in section above helps find the correct threshold values.)

Arduino based camera trigger circuit
Click here to download the full size of the above Circuit.

The momentary push buttons labeled "switch A" and "switch B", and connected to the microcontroller's digital inputs number 2 and 3 (see circuit diagram) are the main user interface with the trigger unit. Pressing these buttons allows switching between the functional states described above. Not shown in the circuit diagram are two BNC plugs that bypass these switches, so that a BNC cable with an attached switch can be used to trigger events from a certain distance to the unit. Outputs from the microcontroller The Arduino's outputs are used to power various LEDs as well as a small piezo-buzzer, indicating the current state of the program. Digital outputs also power the laser diodes, provides TTL logic signals, as well as switch the cameras and the radio transmitter via four optocouplers (4N25, Vishay Semiconductors, Shelton, CT). The following is a more detailed list of the outputs depicted in the schematic circuit diagram. Digital output 4 (labeled "Stim-TTL") is used to trigger the radio transmitter that communicates with the on-board stimulator chip. Depending on the position of switch S1, either a left (OUT1) or right (OUT2) button press on the transmitter is emulated. The connection to the transmitter is optocoupled (OK3 and OK4) to avoid contamination by the very high electrical noise present in the transmitter circuit. Digital output 5 is connected to a buzzer which indicates transitions between program modes with...

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