# Rtcm/voter ttl gps **URL:** \ **Category:** AllStarLink\ **Created:** [December 28, 2021, 8:41am UTC](https://community.allstarlink.org/t/rtcm-voter-ttl-gps/19063 "2021-12-28T08:41:02Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![N5ZR](https://community.allstarlink.org/user_avatar/community.allstarlink.org/n5zr/32/1816_2.png) [@N5ZR](https://community.allstarlink.org/u/N5ZR)\ **Post date:** [December 28, 2021, 8:41am UTC](https://community.allstarlink.org/t/rtcm-voter-ttl-gps/19063/1 "2021-12-28T08:41:02Z")
Can the VOTER take gps input from a TTL GPS? I tried but maybe I am missing a config. -Michael N5ZR ---
**Author:** ![WD6AWP](https://community.allstarlink.org/user_avatar/community.allstarlink.org/wd6awp/32/5_2.png) [@WD6AWP](https://community.allstarlink.org/u/WD6AWP)\ **Post date:** [December 28, 2021, 7:52pm UTC](https://community.allstarlink.org/t/rtcm-voter-ttl-gps/19063/2 "2021-12-28T19:52:15Z")
I’m not sure. Maybe you could lookup the recommended Garmin puck to see if it is TTL. The RTCM accepts Garmin or Trimble sentences and needs 1PPS. Did you find the RTCM/Voter documentation? ---
**Author:** ![Ke2n](https://community.allstarlink.org/letter_avatar_proxy/v4/letter/k/db5fbb/32.png) [@Ke2n](https://community.allstarlink.org/u/Ke2n)\ **Post date:** [December 29, 2021, 8:39pm UTC](https://community.allstarlink.org/t/rtcm-voter-ttl-gps/19063/3 "2021-12-29T20:39:30Z")
It looks to me like a TTL one is what they want. have a look [http://voipvoter.org/voter.pdf](http://voipvoter.org/voter.pdf) seems like they are knocking down the 5 volt to 3.3 volts for internal use. In any case, the Garmin “LVS” model they specify in the manual is sourced at 4.0-5.5 VDC so probably is producing TTL. [RTCM manual](http://173.248.148.139/unode_docs/rtcm_%20manual.pdf) Ken ---
**Author:** ![WD6AWP](https://community.allstarlink.org/user_avatar/community.allstarlink.org/wd6awp/32/5_2.png) [@WD6AWP](https://community.allstarlink.org/u/WD6AWP)\ **Post date:** [December 29, 2021, 11:42pm UTC](https://community.allstarlink.org/t/rtcm-voter-ttl-gps/19063/4 "2021-12-29T23:42:30Z")
I thought you were talking about serial comms TTL vs RS232. Isn’t above +3.3 volts a 1 and .7 or below a zero? RS232 on the other hand is +/-12 volts. ---
**Author:** ![Ke2n](https://community.allstarlink.org/letter_avatar_proxy/v4/letter/k/db5fbb/32.png) [@Ke2n](https://community.allstarlink.org/u/Ke2n)\ **Post date:** [December 30, 2021, 1:08am UTC](https://community.allstarlink.org/t/rtcm-voter-ttl-gps/19063/5 "2021-12-30T01:08:19Z")
Hmmmm, guess I was not clear. I meant the serial comm and pps data from the GPS are reduced from 5 volts to 3.3 volts inside the RTCM. But the main point is that since the recommended serial GPS puck is powered at 5 volts, it’s likely to be providing a TTL signal. There is a USB version of the puck though you would not expect to use that for pps. Ken ---
**Author:** ![N5ZR](https://community.allstarlink.org/user_avatar/community.allstarlink.org/n5zr/32/1816_2.png) [@N5ZR](https://community.allstarlink.org/u/N5ZR)\ **Post date:** [December 30, 2021, 9:44pm UTC](https://community.allstarlink.org/t/rtcm-voter-ttl-gps/19063/6 "2021-12-30T21:44:48Z")
It expects RS232 GPS input as that is what garmin provides. I have TTL GPS units with active antennas and currently use a ttl to rs232 converter. I would like to just provide TTL. I wonder if there are some ports left over on the max232? ---
**Author:** ![Ken\_Jamrogowicz](https://community.allstarlink.org/user_avatar/community.allstarlink.org/ken_jamrogowicz/32/970_2.png) [@Ken\_Jamrogowicz](https://community.allstarlink.org/u/Ken_Jamrogowicz)\ **Post date:** [December 31, 2021, 12:31am UTC](https://community.allstarlink.org/t/rtcm-voter-ttl-gps/19063/7 "2021-12-31T00:31:33Z")
The output of the Garmin is “RS232 compatible” - actual voltages are 0-5 volts just like TTL. None of the pins on the PIC can stand more than about 3.6 volts - hence the resistors at the input. You would probably damage the RTCM is you put a _real_ RS232 signal on it with a +/- 12-volt swing. So the Garmin output is the same voltage range as a TTL signal. But I do not know if the polarity of 1’s and 0’s would be right. Ken > **[GPS\_18x\_Tech\_Specs.pdf](https://static.garmin.com/pumac/GPS_18x_Tech_Specs.pdf)** > > 831.52 KB ---
**Author:** ![N5ZR](https://community.allstarlink.org/user_avatar/community.allstarlink.org/n5zr/32/1816_2.png) [@N5ZR](https://community.allstarlink.org/u/N5ZR)\ **Post date:** [December 31, 2021, 3:58am UTC](https://community.allstarlink.org/t/rtcm-voter-ttl-gps/19063/8 "2021-12-31T03:58:14Z")
Since it runs on a 5V source, i doubt it would produce more than 5V. When i traced the schematic I noticed its going straight to the PIC. Must be something in the code that makes it recognize rs232 over ttl. There is a voltage divider on the RX from the GPS. Maybe reduce that 10k would help. Again though, I see the other side of that MAX3222 is actually tied to ground and could be utilized to convert the GPS to the RS232 the PIC programing wants. ---
**Author:** ![Ke2n](https://community.allstarlink.org/letter_avatar_proxy/v4/letter/k/db5fbb/32.png) [@Ke2n](https://community.allstarlink.org/u/Ke2n)\ **Post date:** [December 31, 2021, 1:43pm UTC](https://community.allstarlink.org/t/rtcm-voter-ttl-gps/19063/9 "2021-12-31T13:43:58Z")
The max3222 produces +/ 13.2 volts using a built in charge pump. Ken