This page is part on a series on the Unicorn EEG system, see also the other posts on the design of the alternative case and wet “sponge” electrodes, and on the native Python interface for Linux and macOS.

Following the design and implementation of the 3D printed case for the Unicorn EEG system, I have had some chance to evaluate it and make some design modifications. The most important is that rather than using the 5×2 shrouded male header ( or “box header”) that needs to be soldered to the 10 tiny wires, I switched to an insulation displacement connector (IDC) version that is clamped on the wires. I still need to squeeze each of the individual wires between the teeth (using pointy squeezers), but that already makes the fabrication much easier. The connectors I used are these, which are similar to these but with “ears” that nicely slot in the sides of the 3D printed enclosure, which also means that no glue is needed any more.

I made 4 so far for various projects and collaborators, all using the standard 5×2 male headers.

Recently we did a demonstration at the Tekniska Museum in Stockholm where visitors could try the EEG out. Combining three different sized S, M and L Unicorn caps (each with its own set of dry electrodes connected to a female 5×2 header) and a single Unicorn EEG amplifier (with the new male header) worked like a charm. The back of the enclosure still has the magnetic mount, similar to the original Unicorn case.

Switching the amplifier by unplugging it from one cap and plugging it into another one without even turning off the amplifier or software made it very easy to maintain attention to the visitors and keep a smooth flow in the EEG demonstration, not having to struggle with reconfiguring the hardware for different head sizes.

This page is part on a series on the Unicorn EEG system, see also the he other posts for a review of the Unicorn Hybrid Black, and the design and prototyping of alternative wet “sponge” electrodes.

The Unicorn Naked comes with the same dry electrodes and electrode leads (wires) as the Unicorn Hybrid Black. However, there is no real advantage of the Naked version over the Hybrid Black version if you want to use them with the same electrodes, unless you insist on a 3-D printed headset to hold the electrodes in place instead of a cap. We figured that the small size and weight, and it being wireless, made it an ideal candidate for developing a wearable system for EEG research on infants and children. At the same time, we sometimes have other applications where a small and wireless ExG system would be useful, for example to record EMG from the muscles or ECG from the heart.

This first image shows the result, further down on the page you can read more on the details and design considerations.

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This page is part on a series on the Unicorn EEG system, see also the other posts for a review of the Unicorn Hybrid Black, and a 3D-printed case for the Unicorn Naked with connectors for EEG, EMG and ECG.

Together with the Unicorn Hybrid Black EEG system that I reported about in another post, I purchased a Unicorn Naked system. It is basically the bare PCB board of the Unicorn Hybrid Black amplifier, including connectors and electrodes, but without the housing and the cap. It comes with a LiPo battery, the cable bundle to connect the electrodes (including the LED strip), a set of 8 dry electrodes, a pack of 50 stick-on electrodes, and a Bluetooth USB dongle. It pairs with the computer just like the Unicorn Hybrid black and uses a unique device name; mine is UN-2022.01.10, which suggests that it includes the date of production and the serial number.

Although it comes with the same g.SAHARA Hybrid dry electrodes as the Unicorn Hybrid Black, the reason for me specifically getting the Naked version is that I want to attach other types of EEG electrodes and also use it for other biosignals like EMG and ECG. For EEG there are four types of electrodes that are common:

• electrode paste, often combined with cup electrodes
• electrode gel, usually applied with a syringe
• wet sponge-like electrodes with saline solution, i.e., salt water
• dry electrodes

The advantage of dry electrodes and wet sponge electrodes over the others is that you can put them on quickly, you can put them on on yourself, and they don’t leave any residue. Electrodes with gel or paste are more suited for a lab environment where a researcher or clinician applies the electrodes to the participant or patient.

However, they all share the same basic physical principles to pick up the potential differences on the scalp due to activity in the brain. Electric currents that flow through the head due to neuronal activity in the brain consist of ionic currents, i.e., these currents correspond to the displacement of positively charged Na+ and K+ and negatively charged Cl- ions. On the other hand, in the amplifier, the lead (wire) and the electrode the electric current is conducted using electrons. The electrode makes the contact with the nonmetallic part of the circuit, i.e., the scalp. The concept of the electrode as the interface between conductive and non-conductive materials has been long known and also applies to fields outside of neurophysiology; the Wikipedia lemma puts this nicely in perspective and provides links to the electrochemistry that happens at the interface.

On this page I present the details and design considerations for sponge electrodes that I constructed myself, based on Ag/AgCl ring electrodes that I had available. The design that I currently consider the most optimal due to its simplicity is electrode design 7. You can find more details further down on this page, including links to the sponge material.

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This page is part on a series on the Unicorn EEG system, see also the other posts on the design and prototyping of alternative wet “sponge” electrodes, and a 3D-printed case for the Unicorn Naked with connectors for EEG, EMG and ECG..

I am exited to report on the Unicorn Hybrid Black EEG headset that I received a few weeks ago and that I have now been able to explore. Together with colleagues from the Donders Institute, the Baby and Child research center and the Body Brain Digital Musical Instrument project we are going to explore this system, both for non-intrusive EEG measurements in young children and for EEG biofeedback for creative musical applications.

The Unicorn is a low-cost 8-channel wireless head-mounted EEG device developed by Gtec and first released in 2019. Gtec has been developing research-quality EEG systems for Brain-Computer Interfaces for a long time, and in recent years have been organizing a series of BR41N.IO hackathons that target hackers/makers and creative applications. I have worked with Gtec systems at a number of BCI2000 workshops, and we used the Gtec Nautilus for the Cogito in Space project (see also here) Given this background, I had high expectations for this new system and the Unicorn does not disappoint.

Unboxing

It arrived in a nicely designed and environmentally friendly cardboard packaging, including dry electrodes, a pack of 50 stick-on electrodes for the reference and ground, a medium-sized cap, an USB Bluetooth dongle and a micro-USB cable for charging. The Bluetooth dongle was not needed to get it working, it also works fine with the built-in Bluetooth of the Lenovo Yoga and Lenovo Thinkpad laptops that I tested it with.

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