- Where can I find documentation on this product?
Version 1 (Green Board) Schematic & Board Layout
Version 2 (Red Board) Schematic & Board Layout
Version 3 (Blue Board) Schematic & Board Layout
Version 4 (Black Board) Schematic & Board Layout
- Connection Diagrams / Write-ups:
- Is there any MORE documentation?
Not at this time. I *barely* had enough time between building boards to create this FAQ page.
If folks would like to contribute any connection diagrams, I will gladly share them or link to them from this FAQ page.
- Will your board work as a single radio hotspot like the ZumSpot board or is it only for repeater?
Yes. It will work simplex. I know LOTS of folks who are doing that very thing.
- Is there Firmware on the board when it ships?
Yes. I load the most current version of the firmware on the board during testing. All boards are ON-AIR tested before shipment.
The firmware I currently load has RSSI and the COS input enabled. (more on these options below.)
- Why does the firmware on my board look REAL old?
The version date of all the software does not change as often as one would think. Jonathan G4KLX only "bumps" the software date when he feels he has crossed a milestone or when he feels there has been enough change to the codebase.
The "build date" is the date the firmware was actually compiled. This date can be found in the DVM "sign on" message in the MMDVMHost log.
In the PiStar image, this log can be found in /var/log/pi-star
- How do I update the firmware?
- Where do I find the newest firmware?
The pre-built binary files can be found here: (There are folders for the different version boards.)
http://dvswitch.org/files/HAM/MMDVM/
- There are LOTS of options at the link above. Which firmware should I choose?
This document expains a bit about the available firmware.
- Is there firmware for your board that supports the NXDN protocol?
Unfortunately the V1 and V2 boards were designed with a processor that is underpowered for NXDN use. Our initial thoughts were that it *might* be OK, but after additional testing it was indeed found to be underpowered. We are actively working on a new V3 (Blue) board that will have an upgraded processor that WILL support the NXDN protocol. Please stand by.
- My board won't go into / stay in BOOT LOADER mode, and thus I can't upload new firmware. Any suggestions?
Depending on the age of your board, pull-up R2 may or may not be populated. If it is not, you might try populating it with a 2.2kΩ
to 100KΩ resistor. According to the specs on the processor a pull-up is not a necessity, however I started populating R2 with a
10kΩ resistor and it has seemingly made it WAY easier to get the processor into boot mode.
If you are still having trouble and running the Pi-Star MMDVM package, try this procedure.
- Why are there no header pins soldered in JP1?
I don't stuff a header in JP1 as it would interfere with the case. (pins stick up too high)
My usual method of shorting the pads is to place a pair of tweezers in the two holes and apply power. Once you are in boot mode (three LEDs on) you can remove the tweezers/jumper and the board will remain in boot mode.
(This is for placing the board in MANUAL Bootloader mode. V3 boards *should* do this automatically.)
- Why doesn't the RSSI input work? (On the RED board)
There is a known issue with the RSSI input.
This issue has now been fixed thanks to Spencer N4NQV. The new firmware image is available at the repository directory listed above.
- Where do I connect the COS pin?
The COS input on the STM32 is *NOT* a traditional "carrier active" input, but rather a "DISABLE" pin. This pin is designed to be used with an outboard CTCSS decoder, or similar, that would tell the DVM to "turn off" when is an analog QSO in progress.
This input is active LOW, meaning if it's pulled to ground, the DVM will go into inhibit mode. ("LED" flashes rapidly)
- My Transmit/Receive doesn't work. Why?
There are two things that can kill the digital receive/transmit: Audio level and polarity. In the RX chain, we can easily get the level set correctly with the on-board "clip light." That only leaves polarity. Transmit/receive polarity is set in the host software running on the Raspberry Pi or equivalent.
If you are running Pi-Star, simply navigate to http://pi-star/admin/expert/ Part of the way down you'll see a section that says "modem." Under that you'll see TXInvert and RXInvert. Toggle RXInvert from a "1" to "0" or vice-versa.
- I don't have time to watch videos showing how to adjust the TX and RX audio. What is the correct procedure?
This procedure assumes you have raw, unsquelched, discriminator noise applied to the RXA input. (no signal)
- The tuning process can be separated into TWO parts: RX and TX (from the node's point of view) For each there are TWO things to be concerned with:
- Level and Audio Inversion.
- Inversion is mostly by trial and error.
- Rx Audio level into the board is easily set by using the "CLIP" indicator. Just set it and forget it for now. The TX audio level going to the radio, not so much.
----------------------RX----------------------
The correct method to adjust the RX audio chain is to turn the Multi-turn gain pot (RX_G) down the whole way. (CCW until it starts clicking - no more than 25 turns) With the gain set to unity (gain pot at minimum) turn the single turn pot (RX_IN) up until the CLIP light comes on, then back it off slightly until the CLIP LED just goes out. If you can't get the CLIP light to come on with the RX_IN pot at full CW, then leave the RX_IN pot wide open and start turning the multi-turn gain pot (RX_G) CW until the CLIP light comes on, then back if off slightly.
Once you have done the above, the DVM *should* respond to incoming digital signals of the protocols that are enabled in the software. If not, you may need to flip the RX invert setting. (PiStar: Config>Expert>MMDVMHost)
If you can't get the clip light to come on with BOTH pots fully CW, there is something wrong with the discriminator input to the board!!
----------------------TX----------------------
The BEST way to adjust the TX level is by using a service monitor or deviation meter. (~2.8Khz on DMR) Barring that, the EASIEST way is to do it via the adjust and test method. First connect to an active reflector that has lots of traffic. While the node is transmitting, adjust the TX pot until the subscriber radio (HT) begins to decode. Keep turning, counting turns as you go, until the radio quits decoding. From that point turn the pot CCW half that number of turns to "center" the level. If you can't get the radio to decode at all, change the invert setting and try again.
- Can TP3 (RXA) and TP6 (TXA_R) be used to set the levels using an oscilloscope? What voltage should I see??
Yes and no. - Yes, TP3 will show you the output of the filtering headed for the A/D converter on the STM32 chip. This should be less than 3.3v maximum with raw discriminator audio to prevent overruns and clipping in the A/D. However, there is a CLIP indicator built on the board that measures the level and keeps it out of clipping. (~3vp-p) So I'm not sure what advantage looking at levels with an o'scope would yield.
Yes, you can look at the output TX level on TP6, but how does that level correlate to overall transmit deviation? That is entirely dependent on the radio/repeater's TX modulator's circuitry. The TX audio level leaving the board tells you NOTHING about over-the-air TX deviation.
- Can I connect an OLED display and where?
Absolutely!! On all version boards these connections will need to be soldered onto the pins of the 40 pin Raspberry Pi mating connector. While these pads of the 40-pin connector are soldered, they are NOT used by the board itself. See this page for more connection information:
https://www.f5uii.net/en/installation-oled-display-ssd1306-raspberry-pi-mmdvm-mmdvmhost/
- Can I connect a NEXTION display and where?
A NEXTION display requires a comm. port. Unfortunately we use the only comm. port on the Raspberry pi's 40 pin interface to talk to the PiHat. Due to limitations of the processor on the V2 (red) boards, there is no way to add a NEXTION serial display other than to an outboard USB to TTL converter plugged into the USB port of the Pi.
On the new V3 (Blue) boards with the more powerful processor, we have been able to take advantage of the "serial repeater" function. This gives a serial port on the DVM's microprocessor for connection to the NEXTION display. There is a specially marked 4-pin header for this very purpose.
Screenshot of Pi-Star Configuration
Official Product of Scott Zimmerman / Repeater Builder
Inspired from a similar design: github.com/wojciechk8/MMDVM_pog
Low-pass filter design by SQ6POG
Images property of Repeater Builder.
Logo Design by Elisha Zimmerman KB9WCX
HTML June 17, 2017 - N3XCC
