Ephys Hardware
A zoomable/editable version of this picture is on Google Drive.
The lab uses microdrives that are not yet documented here. TODO: add section for this part of the rig, and include additional information on specific Omnetics connectors we use.
Electrode arrays are manufactured by Microprobes. Impedance of each electrode should be 4 MΩ, and length is 5 mm. We find that the impedance of the electrodes seems to vary, sometimes significantly. We measure impedance during experiments with a feature in Intan's GUI. The electrode array layout as of 8/27/18 is on Google Docs here.
Hermina Robotka, in the German lab, has been doing some experiments with grounding and shielding to measure how this affects general electrical noise and impedance in the electrodes. It is clear that shielding the electrode array with a faraday cage helps with EMI. You can see some photos of her experiments here (PDF download).
(now optional: 5/1/19 ?!?)
There are two models of Intan Amplifier Boards that have been used in the lab. Currently (5/6/19), we're using the smaller version of Intan's amplifier boards, which digitize and amplify signal from a maximum of 16 electrodes. There is an SPI cable connector on one side (goes up to the commutator), and an Omnetics nano-strip connector on the other side (connects to the electrode array). The Omnetics connector is part number A79041-001 and looks like this:
We also have a larger amplifier board, but we were still using 16-electrode arrays with this larger board (not using half of the pins).
Some of Bill's notes for the commutator wiring are on Google Docs. The commutator we use was built based on plans made by Will Gardner. Documentation for Will's commutator is here.
We have two circuit boards and one "breakout board" in a brown metal box attached to the computer cabinet in 131: the Intan board, the custom voltage shifting circuit board, and the NI SCB-68A breakout board for the National Instruments Data Acquisition card (NI DAQ), PCIe-6321. The NI DAQ card itself lives in the computer's housing, and is connected to the brown box via its heavy cable. The wiring diagram above, shows how the three parts in the brown housing should be wired.
The older version of Intan’s evaluation system is currently used in the lab. We use one SPI input (the connection to the electrode array implanted in the bird); one or two analog inputs (microphone signal from the enclosure); one digital input (signal coming from the PC via the NI DAQ) to correlate auditory stimulae with neural activity; the clock signal; a 3.3V power pin-out to calibrate the Intan board with the voltage shifting circuit; and we ground the faraday cage around the enclosure to the Intan board as well. The RHD 2000 connects to the PC via the USB, and it has it’s own ultra-low-noise power supply.
The RHD 2000 Eval Board has 8 analog inputs that will only accept signals that range between 0V and 3.3V, but most microphones will transmit signals that range into negative voltages (between -5V and 5V, typically). The lab’s custom voltage shifting circuit board takes analog inputs that range between ~ -12V and 12V and shifts and attenuates the signal to be limited between 0V and 3.3V, with high fidelity. It also allows for shielded BNC cables to be connected directly to the voltage shifting circuit board, which is mounted inside a shielded metal box along with the Intan Eval System and the NI DAQ. There are several unshielded connections between the three boards, but they are all housed together inside the shielded box.
The current version of the VS circuit board uses two separate 12V battery packs to power the positive and negative rails of the precision op amp used in the circuit. The battery packs connect with standard 3.5mm barrel jacks.
The National Instruments data acquisition card and shielded breakout board are used mainly to handle audio playback operations: structured auditory stimulae which incites neural activity in the birds. The NI DAQ needs to interface with the Intan board to precisely timestamp audio stimulae with neural activity.
The Frank lab is developing flexible polymer arrays.