FYI - GPS

[F1RMB]

Sorry for offtop.
1. Maybe add support gnss in rt3s version «without gps»?
2. If used none Chinese module, for example ublox max-m8q or max-m10s?

GPS support is enabled in all STM32 devices.
Only the MK22 (GD-77S, DM-1801) has special build for this (as none of them has embedded GPS module, and memory is really limited).
There is a dedicated thread about fitting/replacing module. Basically, the module has to spit NMEA strings at 9600 bauds, TTL level (3.3V).

Cheers.
---
Daniel

[SP2SLU]

Hello. First of all, thank you very much for your contribution to the development of our hobby. I really like this modification. I have retevis rt3s without GPS. My question is just to summarize. What is needed to install GPS? Will GPS work immediately after removing the board and antenna?

[py2pcr]

Now I'm working on the mod to at least keep the almanac until the radio is on. Will write a post about it if/when I finish.
There are some PCB design flaws which make it a little harder to do than I thought.

DISCLAIMER: this mod requires some fine soldering.
I performed this mod and tested it on my radio - but your radio is only yours. Do it at your own risk.

What it does:
It keeps GPSr Vbackup powered all the time the radio is on - thus retaining the almanac regardless of GPS on or off state. This mod significantly speeds-up the re-acquisition when re-enabling GPS.
Also it allows some kind of GPSr Eco-mode as hot-start is now supported - but it's up to developers whether it will be implemented in software or not.

What it does not:
It does not speed-up the first acquisition. Also it does not improve overall GPS reception.
It won't retain the almanac when the radio is powered off. Using the onboard RTC battery for GPSr backup is impractical as GPSr will drain it in 3-4 days. Adding a separate stand-by power supply was considered too difficult for most of the users to implement it.

OK, so what do I need to do?
0. Open the radio, locate the GPSr module on the front panel PCB.
1. Remove the resistor and cut two traces along the red lines.
2. Connect two yellow dots with a thin wire jumper (preferably PTFE-insulated).
3. Connect two blue dots the same way.
IMG_20221221_141223_1.jpg

First, sorry for my poor English...
And thank you very much for the idea!!!! If you have any opinions, I would like to hear them!!!

I am testing this configuration. When I open my RT3S again, I will take some pictures. Now I am trying a micro battery, the same as the RTC, but I am waiting for the new battery (LIR2025 rechargeable from Aliexpress) to arrive.

I think this little bat will be OK if I turn on the radio once a month.

The diode is CUS08F30, which I think retains only about 0.4V or less...

This diode is to be able to recharge the battery when the radio is on. When the radio is off, this GPS will "eat" only 11uA from the battery. In 30 days, it can "eat" 7mAh, and the LIR2025 has about 30mAh. I think these are good numbers.

[VK3KYY]

Why not use the RTC battery already in the radio, or alternative take the supply from the 7.2V battery via an LDO, albeit the LDO will waste main battery power.

[py2pcr]

Why not use the RTC battery already in the radio, or alternative take the supply from the 7.2V battery via an LDO, albeit the LDO will waste main battery power.

I think can work well but the RTC Bat. but the main supply the LDO will "eat" a lot of power, the backup battery pin use only 11uA

[py2pcr]

Why not use the RTC battery already in the radio, or alternative take the supply from the 7.2V battery via an LDO, albeit the LDO will waste main battery power.

I think can work well but the RTC Bat. but the main supply the LDO will "eat" a lot of power, the backup battery pin use only 11uA

If you will use the RTC battery, you need to do this mod to be able to take effect.
I think the RTC battery can survive for 10 days or less.

[VK3KYY]

Why not use the RTC battery already in the radio, or alternative take the supply from the 7.2V battery via an LDO, albeit the LDO will waste main battery power.

I think can work well but the RTC Bat. but the main supply the LDO will "eat" a lot of power, the backup battery pin use only 11uA

Depends on which LDO you use.

e.e.

https://www.analog.com/media/en/technic ... 3007fa.pdf

Ultralow Quiescent Current: max is 7uA, worst case gnd pin current is 350uA

main battery is 2000mA, the LDO would drain the battery in over 5000 hours , approx 8 months.
...

Unless I am not reading the data sheet correctly

[py2pcr]

Why not use the RTC battery already in the radio, or alternative take the supply from the 7.2V battery via an LDO, albeit the LDO will waste main battery power.

I think can work well but the RTC Bat. but the main supply the LDO will "eat" a lot of power, the backup battery pin use only 11uA

Depends on which LDO you use.

e.e.

https://www.analog.com/media/en/technic ... 3007fa.pdf

Ultralow Quiescent Current: max is 7uA, worst case gnd pin current is 350uA

main battery is 2000mA, the LDO would drain the battery in over 5000 hours , approx 8 months.
...

Unless I am not reading the data sheet correctly

This is very good,

I will look into the possibility of buying this model and installing it.

Now my question is, does the OPENGD77 firmware only support GPS and BEIDOU, or will it also work if I install a module that works with other systems?

[VK3KYY]

Yes BEIDOU satellites are supported

[py2pcr]

Yes BEIDOU satellites are supported

but and GLONAS ??, I think I bought a module with glonas too, the firmware will have support or I will need to change it on code?