An EMG-controlled mouse, built in a week
2025 · Team lead · Design and Professional Skills II, UCL
Photo by Vishnu Mohanan on Unsplash
The brief
Build assistive technology that lets someone with limited mobility control a computer cursor using surface EMG, in one week. I led the team.
What I did
We derived the circuit specification from the signal characteristics. Surface EMG ranges from tens of microvolts to a couple of millivolts, with most of its content between 20 and 500 Hz, and the Arduino Leonardo’s ADC reads 0–5 V. This gave a target gain of about 1,500, a 20–500 Hz passband, and full-wave rectification to keep the signal in range.
- Measured gain was 1,705 against the 1,500 target (instrumentation amplifier 35.9× and non-inverting stage 47.6×). The difference comes from the 20% tolerance of E6-series resistors.
- Second-order Sallen-Key high-pass and low-pass filters gave a measured passband of 18.5–482.3 Hz. The active stage reached a −50 dB floor, against −25 dB for the passive stage.
- A precision rectifier inverts the negative half-cycle without losing the 0.6–0.7 V diode drop.
Of the five channels, only two needed strong crosstalk rejection, because the other three had well-separated electrodes. We used active filters on those two and passive filters on the rest, which reduced component count, power and cost without affecting signal quality.
Result
A working interface, from sensing to cursor control, delivered in one week. Graded 91%.