Then things started to get a bit out of hand… Adding in an I2C multiplexer board allowed for more than one RTC module. Since these have a hard coded I2C address you can normally only use one. I went for three – One tracking GPS time, another tracking the rubidium standard, and the last one as a control or reference clock – without compensation.

Notice the new DC/DC converter – It allows input voltages from around 5-30V DC , currently wired into an old HP printer power supply @ 18.5V.