# Heartbeat

![](https://451694785-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MPda5vaSVRKTQ6AoAmb%2Fuploads%2Fgit-blob-5c1fba93b02abee43e4238ca54b8ed9dc3638999%2Fimage.png?alt=media)

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.