# SPARK's fun pulse oximeter and heart rate monitor **URL:** \ **Category:** Qwiic System\ **Tags:** qwiic\ **Created:** [February 26, 2020, 3:04pm UTC](https://community.sparkfun.com/t/sparks-fun-pulse-oximeter-and-heart-rate-monitor/39028 "2020-02-26T15:04:40Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![smp1010](https://avatars.discourse-cdn.com/v4/letter/s/76d3ee/32.png) [@smp1010](https://community.sparkfun.com/u/smp1010)\ **Post date:** [February 26, 2020, 3:04pm UTC](https://community.sparkfun.com/t/sparks-fun-pulse-oximeter-and-heart-rate-monitor/39028/1 "2020-02-26T15:04:40Z")
Dear all, I bought the kit to build a pulse oximeter and a heart rate monitor which contains : A qwiic cable pulse oximeter and heart rate sensor ( max30101 & max 32664) SparkFun RedBoard Qwiic USB micro-B Cable - 6 Foot IC Hook with Pigtail I used it once and scything worked perfectly. However when I tried again it a second time it did not work and I kept getting the error message 255 and it also said that it was not able to connect with the sensor which I noticed because the LED of the sensor did not go on. I wanted to know I any of you had any information regarding this problem. Thank you very much in advance ---
**Author:** ![TS-John](https://yyz1.discourse-cdn.com/sparkfun/user_avatar/community.sparkfun.com/ts-john/32/6093_2.png) [@TS-John](https://community.sparkfun.com/u/TS-John)\ **Post date:** [February 26, 2020, 6:02pm UTC](https://community.sparkfun.com/t/sparks-fun-pulse-oximeter-and-heart-rate-monitor/39028/2 "2020-02-26T18:02:23Z")
Hi, thanks for writing in on the forums. It seems to me that a value of 255 indicates either an issue with the sensors output or there could be an issue with the signal reaching the Microcontroller. I would suggest that you double checking physical connections, especially when using IC hooks and such. If the connections appear good I would suggest testing continuity as a good way to confirm there are no breaks in the wires or other connections. We can start with this step and see what happens. If you could provide a photo of your setup, that would be helpful.