Posted on

Parts for Building a Hotspot Yourself

If you look at the PNWSpot site, and my other blog posts, you will quickly find that I am not going to pretend this is all black magic. Rather, PNWSpots are unashamedly similar to many other Pi-Star based MMDVM hotspots available. Everything from cheap kits on Amazon or eBay, to expensive (maybe even over priced) pre-built hotspots from a number of other sellers.

On the front page of this site, I do list the parts that are used. However, where are they purchased, what exact units/models are they? That’s what this post is here to answer, as well as give some alternatives and suggestions.

The Components

Most, if not all Pi-Star based MMDVM hotspots have the same components:

  1. Raspberry Pi (Usually either a Zero W or a 3B)
  2. MMDVM “Hat”
  3. OLED Screen
  4. Micro SD Card flashed with Pi-Star
  5. Case of some sort
  6. Antenna of some sort

Component Deep Dive and Recommendations

Let’s take the list above, talk about each component and give some recommendations and sources:

The Raspberry Pi

For this, you have two main options. A Raspberry Pi Zero W, or a Pi 3B+. You can use a Pi 4, but it’s really not needed.
If you are not super comfortable with soldering, you may want to get a Pi Zero WH (With Header), which comes with the GPIO headers pre-soldered. The Pi 3B+ also comes with the header soldered.

Pi Zero:
Zero W: https://www.adafruit.com/product/3400
Zero WH: https://www.adafruit.com/product/3708

Pros: Small, Cheap
Cons: Slower (Not really a con, do not need the hotspot to be fast for the basic task it is performing)

Pi 3B+
https://www.adafruit.com/product/3775
Pros: Faster
Cons: Bigger, More Expensive

The MMDVM “Hat”

This is where all the magic happens. This is what makes the hotspot a hotspot. The MMDVM board is what transmits and receives (along with a number of other functions). This is where you have a number of choices, both cheap and expensive.
You can absolutely get random boards off eBay or Amazon, however these do not always work perfectly and are all more or less basic clones of an original design. The cheap ones you see on Amazon or eBay are usually referred to as “JumboSpots”. The boards I will recommend below have good track records, and most I have used myself.

Simplex vs Duplex? This is a question that you may have now that we are talking about the MMDVM Hats. To make it simple: If you are a heavy DMR user, a duplex hat will let you use multiple timeslots simultaneously, and also let you “interrupt” a conversation to switch talk groups. If you are not a heavy DMR user, there are pretty much no benefits to spending the extra $ on a duplex board.

Pi Zero Hats:

BI7JTA Simplex MMDVM Hat:
https://www.bi7jta.org/cart/index.php?route=product/product&path=59_64&product_id=69

This is the primary hat that I use in PNWSpot hotspots. Winters (BI7JTA) is a Chinese ham who builds and sells these boards. They work flawlessly, have modifications by him to improve the design and operation, and you are supporting a fellow ham with your purchase. The biggest “Con” is waiting for the shipping (usually 1-2 weeks depending on what speed you pay for).

These boards come with a 432MHz SMA antenna with the SMA connector pre-soldered to the board. However, you can also source and install a ceramic antenna directly to the board if desired. You also have the option to have the OLED Display pre-soldered.

N5BOC Simplex and Duplex MMDVM Hats:
Simplex: https://www.store.n5boc.com/product-page/mmdvm-simplex-1v8
Duplex: https://www.store.n5boc.com/product-page/mmdvm-duplex

David Dennis, N5BOC has two very high quality MMDVM hats. One is a simplex hat that actually has an internal antenna by default (you can add SMA if desired), as well as a duplex hat. The description from David’s site explains some of the improvements he has made to the design:

…this board has its own dedicated 3.3V regulator and does not pull voltage off of the noisy Raspberry Pi 3.3V line like all other simplex board do. This board is now a 4 layer board with LARGE ground planes for 3.3V and GND sandwiched in the middle. This acts as one very large decoupling cap the size of the entire board. Also this isolates signals between TOP side and BOTTOM side. Speaking of that all of the Analog RF signals are on the TOP side only and the high harmonic digital signals are all kept isolated on the BOTTOM side. Making this board much more stable. It should also make it more sensitive on receive.   

The SIMPLEX board comes with a 432MHz ceramic antenna mounted on the board.   But if you prefer you can dismount this antenna and install an SMA connector in order to install a standard antenna with some gain. The DUPLEX version has two SMA Connectors and you can choose to add two SMA antennas to the order if needed as well.

Pi 3B+ Hats:

You can technically use most Pi Zero hats on a Pi 3B+, the problem comes when you look for cases. So to be safe, if you plan to use a Pi Zero MMDVM Hat on a Pi 3B+ and want to use a pre-made case, keep it to the simplex boards.

If you do want duplex, get a board designed for use with the Pi 3B+, like the one below

BI7JTA Duplex MMDVM Hat:
https://www.bi7jta.org/cart/index.php?route=product/product&path=59&product_id=50

Winters (BI7JTA) is a Chinese ham who builds and sells these boards. They work flawlessly, have modifications by him to improve the design and operation, and you are supporting a fellow ham with your purchase. The biggest “Con” is waiting for the shipping (usually 1-2 weeks depending on what speed you pay for).
These boards come with a 432MHz RIGHT ANGLE SMA antenna with the RIGHT ANGLE SMA connector pre-soldered to the board. If you plan to use one of the standard Duplex MMDVM Pi-3B+ Cases from C4Labs as mentioned below, be sure to tell Winters to send you a board with Vertical/Straight SMA connectors soldered to the board, NOT right-Angle. You also have the option to have the OLED Display pre-soldered.

The OLED Display

0.96″ OLED Display
https://www.amazon.com/dp/B00O2LLT30/

If you buy an MMDVM hat from Winters, BI7JTA above, you can get an OLED display pre-soldered by him. If you want to install yourself (Like I do), or, want to use a different MMDVM board, you will need to search Amazon or eBay for a 0.96″ OLED display with the pins in this order:
| 3.3V+ | GND | SCL | SDA | Many do not come in this order, so just be sure to check!
One thing to note – having a display is absolutely NOT necessary for operation. There are blinking LED’s to display the status, and of course, your radio’s display which will show callsigns and possibly names.

The SD Card

Sandisk or Kingston Class 10 MicroSD Card
https://www.adafruit.com/product/2693

This one is simple. Get a 16GB Class 10 or better MicroSD card from a reputable brand. I use units from Kingston or Sandisk.

The Case

C4Labs
Pi Zero Simplex: https://www.c4labs.com/product/zebra-jumbospot-pi-screen-case-raspberry-pi-zero-zero-w-jumbospot-color-and-top-options/
Pi Zero Duplex: https://www.c4labs.com/product/zebra-duplex-pi-zero-screen-case-raspberry-pi-zero-zero-w-mmdvm-duplex-color-and-top-options/
Pi 3B+ Simplex: https://www.c4labs.com/product/zrpi-1as-case-for-raspberry-pi-3-b-and-zumspot-with-attached-1-3-oled/
Pi 3B+ Duplex: https://www.c4labs.com/product/zebra-duplex-pi3-screen-case-raspberry-pi-3-b-mmdvm-duplex-black-ice/

Basically, if you want a great case, just buy one from C4Labs. These are the cases I use for PNWSpot hotspots.

Other Cases
If you want, you can also 3D print cases, or, get cheap metal and acrylic cases from eBay. I am not including any links for eBay, as they are often changing and I really have no experience ordering from the sellers so I cannot vouch for them. In my opinion, unless you plan to modify a normal raspberry pi case or build your own, you might as well buy a case from C4 labs.

The Antenna

99.9% of the time you will be getting an antenna along with the MMDVM board your purchase. If you don’t, most 70CM Ham band SMA antennas will work, however you may need extensions or other adapters to get them to fit with the cases.