> For the complete documentation index, see [llms.txt](https://learn.arduinosa.co.za/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://learn.arduinosa.co.za/sensor-kits/37-in-1-sensor-kit/heartbeat.md).

# Heartbeat

![](/files/-MS2NiHx6YIE2upIjxZI)

This module consists of an IR-LED and a photo transistor which can be used to read a pulse when a fingertip is positioned between the LED and photo transistor. The module requires additional external circuitry. A 330 ohm series resistor for the LED is included. The 5 V supply connects to the centre pin, ground to the ‘-’ pin. The photo transistor signal is available on the ‘S’ pin which has a built-in pullup resistor.