Welcome to INSight, the open source infrared neural stimulation system! Here you will find design documents, code, and bill of materials to build your own INSight. Questions can be made in the Issues section of this respository.
If you use INSight, we only ask that you cite our paper: https://doi.org/10.1093/pnasnexus/pgae082 and repository https://doi.org/10.5281/zenodo.11086673 and consult your institutional laser safety officer to ensure INSight is used in safest conditions possible.
Building insight is a quick and easy build, but should follow a defined set of steps. The steps are as follows:
- Build/Populate PCB without driver and laser diode
- Test PCB
- Mount Laser Driver
- Driver testing with dummy load
- Placing laser diode
The first step is to obtain a PCB. The included Gerber files can be directly uploaded to OSH Park for fabrication. Other fabricators (Express PCB, etc) can be used just as easily. Alternatively, if access to a PCB milling machine is available, the PCB can be fabricated in house. In fabbing in house, after completion a short check is warranted to insure laser diode current lines (large traces) do not short to 5V rails, which will cause the laser diode to fail.
Once the PCB is milled, place all components with the exception of the laser diode driver. Use good soldering techniques and ensure no dry solder joints have been made. Place pogo pins in pins designated for the laser diode. The 5V in header should be populated with the 2 terminal screw terminal, and outputhubs 1-2 populated with the 6 pin headers.
Once the PCB is populated, test that 5V is going to laser diode driver pins. A warning, the power supply is capable of sourcing large amounts of current, so care should be taken to ensure no connection of the circuit can be made to your body. Using circuit PPE is warranted here. Connect the power supply and switch the circuit power switch to on (labeled POWERON on board). Using a multimeter, measure the + probe to pin 13 hole and the - proce to pin 12 hole of the laser diode driver. Voltage should read 5V. As this is regulated, if voltage is significantly different than 5, check solder connections of the 5V regulator (LM7805). If this is successful, move to the next step.
Next, solder the laser diode driver to the interface PCB. Make sure Pin 1 is in the correct place the rotating the PCB to match the orientation shown in the INSight.png file, with info text in the upper right and power switch on the lower left hand side of the board. Pin 1 on PCB is the lower left pin of the laser diode driver component on the PCB. Solder joints should be made quickly to ensure heat build up on the PLD10000 is minimal.
In order to test the laser driver before hooking up the laser diode, create the circuit given in testload.png, ensuring that the resistor can source atleast 2W. Before beginning, note that improper use can result in quite a large shock. All safety precautions must be followed. Connect LDA to the LDA pogo pin and LDC to LDC pogo pin. Set the laser diode driver to constant current mode, and follow the instructions for testing wavelength electronics drivers here: https://www.teamwavelength.com/test-load-basics/ Be sure to follow instructions for constant current mode, as this setting will be what INSight primarily operates in. During this stage, the laser current limit can be set to ensure current does not exceed maximum current of Akela module. We suggest 90% of max as the limit. Once done, turn current setpoint to 0 leaving current limit to 90% max.
Once all tests have been passed, attach the Akela laser by placing pins onto pogo pins and screwing the device in using screw holes on the side of the device. No soldering should be done here, as excess heat will damage the device. Furthermore, this allows for the diode module to be swapped. Before turning on and arming the laser, ensure pins line up with the akela pinout provided. Pin 3 should align with LDA, and pin 8 to LDC. If pins are swapped, the laser will be damaged. It is recommended that the laser is tested using a power meter with the fiber optic fully enclosed and all PPE and laser safety googles worn as stray beams, even at low powers, can cause damage to the eyes. Turn on the power or energy meter. Turn on the power supply and laser PCB. Double checking that all safety measures are in place, slowly turn the output adjust till a laser power is measured. Using a multimeter and the PLD10000 transfer function, check for errors between Akela datasheet power to current relationships. Once complete, turn set point to lowest value just below power/energy meter detectability.
To provide modulation of the laser, analog outputs of other hardware can be used. Analog + is attached to Pin 4 of Outputhub 2 (see board). Analog - is attached to the low current ground, Pin 1 of outputhub2. Check the included PLD10000 transfer function for input voltage to output current relationships, using the above testing procedures to ensure laser power is what is expected from current to output power curve of the Akela.
LaserControl.ino is for controlling the Laser node in response to an external trigger. To use this code, you will need an Arduino Due, or a similar arduino with an onboard digital to analog converter. Simply load this code onto your device using the Arduino IDE (webbased or computer based are equally good) and load in your randomized stimulus values into the variable outVoltages. Note that this code will repeat for as long as it has a input trigger.
As programmed, the arduino expects a LVTTL pulse (0-3.3V) on digital I/O pin 7 to send voltage waveforms to the pulser. A pull down resistor of 10k should be connected to pin 7 to ground to ensure pulse stability. LVTTL pulses should be brief, shorter than the total run time of the stimulus train to ensure no repeated stimuli occur.
The laser pulser analog in (or similar on other pulsers) should be attached to DAC0 on the DUE and grounds tied together. DAC0 has an output range of 0.5 - 2.8V, so voltage dividers on output may need to be added to get output voltages in the desired range.
This laser, like all lasers, uses high electrical currents and wavelengths which can be damaging to the body. Always practice good PPE and high current standards. Before use, consult with the institution laser safety officer to ensure the space and preparation is ready for laser use. If any questions arise, consult an institutional staff electrical engineer or laser safety officer. It is expected that laser safety googles which have been rated for the wavelengths used are worn at all times laser is on, or is about to become active.
Safe laser usage relies on both engineering controls and explicit protocols which are available to all users of the lasing system. To facilitate good practice, a laser standard operating procedure template is included in this toolkit which can serve as a baseline for development of user SOPs. This template must be adjusted to suit the needs and requirements of the institution in which INSight will be used.
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