DMR Hotspot
Duplex Solar
A duplex MMDVM hotspot with a Nextion screen, two 18650 cells and a solar panel, so it runs for days away from a socket.
It all started with the fact that I decided to have my own DMR Hot Spot, frequent trips and lack of coverage for DMR converters are the main reasons why I bought the MMDVM duplex plate.
Another reason for building a solar hot spot was that I bought the board itself without the housing. When I started to choose the housing, I dreamed to have at least two 18650 batteries inside so that I would not have to remember about the power bank. Studying a lot of articles on the internet about powering the Raspberry Pi Zero through a 18650 battery, I came across many solutions including recharging the battery using a photovoltaic panel and decided to try to build just such a hot spot so that you can work on battery power for at least 2 days and, by the way, be able to recharge it without using a wall charger.
By the way, I came across numerous projects regarding the use of NEXTION screens for five star; after checking the dimensions of such a screen, I ordered one without waiting long.
For the project I used a voltage stabilizer so that the Raspberry Pi was powered evenly with 5 V. Unfortunately the 18650 battery alone gives less than 5 V; the tests showed that this solution could also work, but the DC/DC converter was very cheap so I also bought it.
After connecting everything, I also added a fan, but now I think it is unnecessary: quite large holes for the antennas allow you to keep the temperature below 50 °C. Additionally, I added the main power switch and a Nextion screen off switch if you need to save battery.
After putting everything together, it occurred to me that I could not check the level of battery discharge, so at the end I also added an LED indicator to control energy consumption.
The whole thing, despite being built in the evenings, came out quite neat and most importantly it works very well both on trips, in the car or in the field. Even setting the DMR hotspot against the sun for charging did not significantly increase its working temperature. Of course, using the TP4056 charger I also have the option of charging the 18650 via a wall charger.
Materials
- Raspberry Pi Zero W
- 2×18650 pack, 3400 mAh each
- MMDVM MicroRepeater / Dual HotSpot hat for RPi
- TP4056 charger
- MT3608 step-up converter
- 6 V solar panel
- 1S LED battery level indicator
- 5 V 25×25 mm fan
- 2 slide switches
- 1 power switch
- 110×75 mm enclosure
This is a set that can of course be adapted to your requirements or even the housing, e.g. increasing the number of batteries or the size of a solar panel.
