Garmin v1.0b manual Optional PPS Active Indicator

3)Gently pry the old microcontroller from the socket, and insert the new PIC16F688.

4)Finally, the 12V DC power adapter will need to be replaced. WARNING: the 12V power adapter which shipped with the non-GPS kit is transformer based, and provides too high a Voltage for the GPS modified clock. The transformer based power adapter can actually output up to about 18V, which will burn out the 100Ohm dropping resistor. Please make sure to use the GPS modified clock ONLY with a switch- mode 12V power adapter, a 12V battery, or other true 12V source. The 12V power adapter included with the GPS upgrade kit is a switch-mode power supply which will work without problems.

Jumper Wire

New 100Ohm,

1Watt

Resistor R1

Optional PPS Active Indicator

5)Optionally, although recommended, you may wish to run a jumper wire from the AUX_A pad to the decimal point indicator on the seconds nixie. This will light up the decimal point on the right hand nixie as long as PPS signal has been received from the GPS within the last second. Remember that the GPS takes about five minutes to get synchronization on power-up before the PPS signal will be received.

The decimal point pins on the nixies are directly to the left and right of the bottom- most pin- approximately in the 5 o'clock and 7 o'clock positions. You can use any decimal point you wish as the indicator.

The AUX_B pad can also be used, except this pad will toggle on or off each time a new pulse is received on the PPS line. The effect of connecting to the AUX_B pad is the indicator will turn on for a second, then off for a second, and then repeat so long as the PPS signal is active. If the PPS signal stops, the AUX_B connected indicator will maintain it's last state.