Electrode Interface Fixture (EIF)

© 2023, Kevan Hashemi, Open Source Instruments Inc.




[07-SEP-23] The Electrod Interface Fixture (EIF) mounts permanently on the skull of a subject animal. The EIF mates with a Head-Mounting Transmitter (HMT) such as the Head-Mounting Transmitter (A3040). It provides two or more electrical connections between the HMT and animal biopotentials, most often EEG, ECoG, and LFP.

Figure: Electrode Interface Fixture (EIF8-XAAX).


[07-SEP-23] Each EIF consists of a connector and a number of wires leading from the connector. Each wire has a termination. The EIF part number takes the form EIFn-L, where n is the number of contacts on the connector and L is a string of one or more letters that defines not only the number of contacts used, but also which contacts are used, the type of wire on each contact, the length of each wire, and the termination on each wire.

Version Connector Wires Terminations Compatible Transmitter
EIF8-XAAX PZN-08-AA 5 Silicone-Insulated Helical Steel 2 X-Electrode, 3 Bare Wire A3040D
EIF8-S PZN-08-WC 5 Teflon-Insulated Stranded Steel 5 Bare Wire A3040D
EIF8-M PZN-08-WC 5 Teflon-Insulated Solid Silver 5 Bare Wires A3040D
Table: Electrode Interface Fixture Versions.


[07-SEP-23] Each EIF is built around a connector. Sometimes we buy the connector with the wires loaded, and cut off the wires we don't need. Sometimes we solder the wires onto the connector ourselves and terminate them with depth electrodes. Here are data sheets for the connectors we use in our fixtures.

A79614: PZN-08-AA, 8-way connector, vertical, through-hole.
A78914: PZN-08-WC, 8-way connector, stranded 316SS leads.
A78967: PZN-08-WC, 8-way connector, solid silver leads.

The PZN-08-AA and PZN-08-WC are miniature, polarized connectors. Here is the pin numbering scheme we use for the connector.

Figure: Electrode Interface Fixture (EIF8) Connector. Left: Top View. Right: Bottom view.

The EIF8-S starts off as a connector loaded with eight wires. We remove those that are not needed, cut short those that remain, and strip the insulation off the final 2 3 mm of each lead.

Figure: PZN-08-WC with Stranded, Stainless Steel, Teflon-Insulated Wires.

The EIF8-XAAX is a complex electrode with five wires, each of which has its own color and termination. The table below presents the color coding.

Table: Color Codes, Pin Numbers, and Functions of EIF8-XAAX Wires.

The "GND" connection is "Signal Ground". Once we connect this potential to an animal body, we say the HMT is "grounded".

The EIF8 pin numbers in the sketch match the pin numbers of the mating connector on the HMT circuit. So we have Pin 1 and 2 are GND. We have X1, X2, X3, and X4 on pins 7, 4, 3, and 8 respectively.