Biopotentials are generated by physiological signals of our body. These signals are generated due to electrochemical activities of certain types of cells present in our nervous, muscular and glandular body parts. They can be classified as ECG, EEG, EOG, etc. These signals are translated from our body onto the output devices using a signal acquisition device. If you are interested in Biosensing can read more about it here.
Signal acquisition process
Today, we are going to understand one such open source module, understanding all the nuances, complexities and challenges they undergo in designing and manufacturing the successful biopotential module – BioAmp EXG Pill by Upside Down Labs.
BioAmp EXG pill (H6 heading)
It is a 2.5cm x 1.5cm biopotential Analog Front-End (AFE) signal acquisition device that senses and amplifies bio signals. The signals are received via this pill sized BioAmp module and transmitted to the Micro Control Unit (MCU) via Analog-to-Digital Converter (ADC) which can be further used to control various actuators or devices. This module is compatible with Raspberry Pi Pico, Raspberry pi 3/4 (With external ADC), Arduino and other microcontrollers. People from UpsideDownLabs have give some great example using BioAmp EXG Pill, like Music generated from EEG, Controlling servo with EMG signal and more.
Features & Specifications
- Input Voltage: 4.5 – 40 V
- Input Impedance: 10^12 Ω
- Compatible Hardware: Any ADC input
- Biopotentials: ECG, EOG, EMG, and EEG (configurable Band-Pass)
- No. of channels: 1
- Electrodes: 2 or 3 (configurable)
- Wearable: Yes
- Dimensions: 25.4 x 10.0 mm
- Designed for Use With a Carrier Board: Yes
- Open Source: Hardware + Software
You can do variety of bio sensing with just one BioAmp EXG Pill board:
The Experts on Field: UpsideDownLabs
UpsideDownLabs(UDL) specialize in creating DIY electronics devices working in the domain of neuroscience such as BioAmp Devices catalogue which distributes BioAmp version 1.5, Muscle BioAmp Candy, Muscle BioAmp BisCute and Muscle BioAmp shield.
They are work on making affordable open-source hardware and software solutions for:
- B2C Model, catering new learners, enthusiasts, researchers, etc.
- B2B Model, by making the technology development cycle efficient for the corporations.
BioAmp Pill: Unwrapping the Design
Thought Process behind the Technology – UDL developed the underlying technology from scratch. It uses a discrete 1000x Gain(bandpass) amplifier circuit built with Texas Instruments TL074 quad low-noise JFET-input general-purpose operational amplifier in a TSSOP-14 package. Since, the amplication done on the board is in Analog in nature there were more calculation involved to get the active bandpass filter up and running to give accurate results. Most of the filtering and cleaning the signal is done on the firmware (which is open source too). If you like to further learn about the firmware, filtering and calculation, check out the UDL YouTube channel.
BioAmp EXG Pill Circuit
Even though the technology seems very simple. In terms of getting the prototype, a huge cost and physical labour are undergone. There were multiple prototypes which were developed, tested and rejected by UDL to finally arrive at this current version.
Printed Circuit Board Design and Development – The BioAmp EXG Pill is a two layers PCB designed using KiCad, where all the components are placed on one side and have various configurable options (gain, filter, electrode, band pass) on the back which can be adjusted through jumpers.
Front View of the PCB
Back View of the PCB
Apart from being used as a ready-to-use out of the box module, Gold plating and Castellated holes are done on the bio amp pill (even if it increases the cost) to give a better finish that HASL(Hot Air Solder Levelling) and easy to mount on a host PCB as a chip. This is further coupled with compact design allows functioning in both mobile and space constrained projects hence, widening its application pool.
BioAmp EXG Pill
Its designed is such that it makes the functioning hassle-free by it’s elegant and thoughtful design. Which allows it to be used in three ways:
- Its pin-header holes allow you to solder (berg strip) pin headers for easy use with a breadboard
- Its castellated holes allow you to solder BioAmp EXG Pill directly onto a custom PCB that requires biopotential-amplification capabilities
- Its electrode holes allow you to use any 1.5 mm diameter wire as an electrode cable with minimal strain
PCB Layout BioAmp EXG Pill
The complete BioAmp project was done using open source software like KiCad, Blender, Inkscape and Gimp. Since all the software are open source, it can be downloaded by anyone for free and access all design files of the BioAmp project from the GitHub repository to modify them according to the requirements or manufacture it on own.
Shortcoming of Open Source Product
As we spoke to Deepak Founder of UDL, we understood the one of the major short coming of open source products. Due to availability of hardware and software designs is open source, many have replicated their design and manufactured PCB without giving proper credit to UDL. So, we highly recommend if you are planning on manufacturing the board or use their design it would be great to give proper credits to UDL or buy directly from them. [Purchase – link]
Cost of BioAmp EXG pill
One BioAmp EXG Pill module is around ₹2,600(~$33), it includes cables electrodes, the BioAmp EXG Pill itself and plus the software is open for all which can be access through there website. If you are students we highly recommend to contact them to get a discounts on the product, where the BioAmp Pill kit (BioAmp EXG Pill boards, Gel electrodes, 2 x 3-pin angled & straight header pins, and 1 m BioAmp cables.) generally cost ₹5,200(~$66) for everyone, for students they are providing the kit for around ₹4000(~$50). [Purchase – link]
When asked about the high cost of the product in comparison to their other products, the Deepak explained the challenges faced. One major reason is resourcing various components in post-covid and chip shortage era which has hampered the supply chain distribution. So, passive components (like resistors, capacitors) which are easy to get but there is high demand in resourcing the main amplifier TL074, Which increases the cost of production. Also when checked for better alternative there are no better match for main amplifier like TL074 because of there excellent noise cancelling at such price point when compared to other available at that same price.
However, they are working on ways to cut production costs in the coming months.
Further, UDL suggest a work around to keep things less expensive by buying one of there alternative product – Muscle BioAmp Candy which works similar to BioAmp EXG Pill, but of course cutting down on the amount features provided.
Upcoming New Products in Pipeline
Muscle BioAmp BisCute, which will be announced very soon.
Muscle BioAmp Candy, which was launched a couple of months back but manufactured in small quantities to test the market went out of stock very soon, so they are manufacturing it again and will be available soon via online sources. BioAmp Patch, it is a replica of myoware sensor, it’s kind of a patch where 3rd electrode comes out of the device. It will be at a reasonable cost of around ₹1000(~$13) only.
They are also planning to go to EUG, ECG and EDG devices in the coming months with a target of furnishing a whole catalogue in the domain of DIY neuroscience.