I’ve been a fan of screwing around with the MMDVM hotspots ever since I picked up a ZumSPOT with my D74. Though I remember them being around when I got in to ham in 2015; they’ve gotten a lot cheaper and a lot more universal.
Anyway; I upgraded one of my hotspots and did a neat little trick with my now spare MMDVM HAT.
Simplex operation is all fine and dandy, especially since you can just run on simplex frequencies; and all of the modes can be made to run in a simplex (or simplex-like) configuration with no issue. But you do get some additional features with DMR when operating duplex; largely the ability to run dual-timeslots.
Duplex hotspots aren’t exactly new; but they haven’t been around nearly as long as simplex variants and they are pricier. The main advantage to having dual time-slots is I actually get the confirmation tones when I key-up a talkgroup; which in itself is almost worth the price of admission to me.
Yes..it is probably one you’re going to complain isn’t a Zum; but here’s the thing…as I like to experiment with things; I’d rather blow up a cheap board than the good one. It’s like I don’t really care for Baofengs other than a situation where the radio will likely get destroyed.
Anyway…I was rather surprised to find this one came pretty much pre-assembled; which is still somewhat annoying as I don’t really need a display. At some point I’ll have to desolder it and replace it with a proper connector of some sort; then steal the OLED for some other project…or at the very least swap it out with the smaller “Type 3” OLED since I have one in a box somewhere.
Upgrading was largely a matter of just plugging the hat on to the PiZero, booting Pi-Star, and setting it for the new modem and other related stuff. Then after rebooting to make sure all the settings worked.
Even on the outdated 3.4 version; this worked fine. Brandmeister picked up that I’ve now got two timeslots and let me set some group assignments. I’ve been able to use both slots as expected; though I’m considering picking up a second cheap DMR HT just to see how well dual time-slot works on the thing.
But what about the simplex board I was running? Well, I do have a Fusion radio that’s been sitting here in the shack. It used to mostly live in my car as part of my mobile setup with a small V/U amp; but since last year’s incident where I lost both the mobile setup and the car, it’s been here. I haven’t played with Fusion a whole lot due to the fact…I just haven’t. We have a Fusion repeater in the club; but it’s WIRES-X computer was always in various states of not working. (Which is fine because WIRES-X is a PITA.) Since it primarily lived in my car; the D74 saw most of the hotspot action. I did however use my FT2D quite a bit playing around with DMR cross-mode operation. In fact most of my Fusion radio usage with this thing was largely to test things so I could demo/explain to others.
But I did something different.
Can you run an MMDVM on an Arduino? All depends on what you consider Arduino to be. Can you do anything with the ATMega on an Arduino board? Probably not. I can’t imagine a lot of situations where it’d have the power to do anything. But can you use the USB-to-UART on an Uno R3 board to talk to it with your PC? Yes. Yes you can.
Hopefully you noticed a lack of ATMega328 in that thing. I pulled it out some time ago to use as a serial adapter and I can’t remember where I put it. I’ve got another…and a Mega2560 so I can just burn new blank MCUs. But I’m going off on a tangent. What you’re looking at here is an MMDVM (which turned out to be one of the ‘JamboSPOT’ clones) board with some jumpers jammed in to a bare Uno R3. Blue and green provide serial data; red and black are 3.3v power. Sure, it still identifies as an “Arduino Uno” in device manager…but that doesn’t matter; as long as we have a COM port we can do this:
So, for the time being (from my research operating a simplex node is legal by 97.201 definitions)…at least untill Field Day…I’ve got this working. It worked very well for days too; so not bad.
But…I gotta get goin on Field Day now.