The Tandy Multiface is a brand new I/O interface board for the Raspberry Pi designed by Darren Grant from Tandy.
The reason it came about is that, back in September 2012, Tandy was marketing a Gertboard kit, having bought a supply of official Gertboard PCBs from Farnell. This was a bit of a coup because Tandy beat Farnell to the punch with their own product. Farnell struggled to get their ducks in a row (I seem to remember comments about a shortage of one of the chips) and launched their kit about a month later.
So it wasn’t a complete surprise (to me at least) when, a little later on, it was announced that the bare boards were no longer available and Farnell discontinued the Gertboard kit in favour of a pre-assembled board.
A bit of self-indulgent speculation
This next part is pure speculation on my part.
[speculation on]I have no inside knowledge of this, but it looks to me like they tested the market with a kit. Then, having proved there was a market for it, decided it was worth investing in production. Either that, or they wanted to ensure exclusivity – or both.
Part of the original aim of the Gertboard was to get people into hardware. Gert spent a lot of time on the assembly manual and a series of soldering videos. It’s clear both from forum comments and just looking at the way things turned out that there was a change of direction which was more than likely commercially driven.
I want a kit!
But there was, and still is, demand for a kit. So Darren designed a compatible board of his own, with through-hole only parts – so no surface-mount soldering. The result of this is the Tandy Multiface, which is pretty much pin compatible and functionality compatible with the Gertboard.
If you’ve soldered before, it should take you a couple of hours to put one together. If you haven’t, it might take up to four hours. But it’s not a scary experience at all.
The video shows a 2 minute walkthrough of the board’s contents. There’s a lot more detail in the text below it. Actually, I suggest you read on then come back for the video.
The Multiface board is designed to sit next to the Pi and is connected by a short ribbon cable. The nice thing about ribbon cables is that you can use one of whatever length suits you. If you prefer a socket, you could easily mount one under the board and add some “feet”. Because it’s a kit, you have that choice.
What are the differences between Multiface and Gertboard?
The three most obvious differences visually, when you look at the two side by side are…
1) the Multiface is slightly larger – because through-hole components are larger
2) there’s no prototyping area on the Multiface
3) The buffer direction settings are all in one place on the Multiface
Other differences are…
4) Multiface uses a ribbon cable, whereas the Gertboard V2 sits above and adjacent to the Pi via a direct socket connection.
5) Multiface has a “power on” led, which is constantly lit when power is connected. This is a nice additional feature. (Gertboard V2 leds are all lit when powered up unless pulled down.)
6) Multiface has an auto-resetting fuse instead of one which can blow and need replacing if you mess up with the motor.
7) The way that the motor controller is implemented. Multiface has a 3 pin arrangement, one for enable, one for MOTA and one for MOTB, whereas Gertboard uses two pins MOTA & MOTB.
For the final edition, Multiface has no “J7 jumper” which has caused quite a few queries on the Pi forums. (People don’t read instructions and assume an assembled board is ready to go, but they need to apply a jumper before Gertboard will work properly.)
What about the chips?
All the integrated circuits (ICs) are socketed, just like the original Gertboard kit, which makes it easy to replace a chip if you damage it. All the ICs are the same (or equivalent) as the ones on Gertboard, with two exceptions…
- The motor controller is a different chip. Gertboard uses Rohm BD6222HFP, Multiface has SN754410NE
- The Darlington Array is also a different chip. Gertboard uses Toshiba ULN2803, which has 8 ports on, but only 6 are used. The Multiface has a ULN2003 which is the seven port version, and all seven are in use. So you have 7 open collector ports on the Multiface and 6 on Gertboard.
Apart from those two differences, the ICs are the same.
- 3 bidirectional 4-way buffer chips
- ATMega 328p
- ADC MCP3002
- DAC MCP4802
What about the software?
- One to the open collector program to make the 7th Multiface port available. Although the way this program works it’s only a change in the wiring instructions since only one port at a time is tested with one wire from GPIO 4.
- One tweak to the butled program wiring instructions because of a discrepancy in the pinouts on the buffer 3 I/O select header (Multiface pin 2, Gertboard pin 1).
- Possible tweak to the motor program to make full use of the three pin arrangement (although the existing motor program works ‘as is’).
- Small tweak to wiring instructions for ADC/DAC programs as less jumpers are needed on the final version
(Update: I’ve tweaked all the software so that the correct pin names appear in the wiring instructions for Multiface. You just run each program as
sudo python program_name.py m the extra “m” on the end tells the program you want the Multiface version. This software will be released before the Multiface is launched.)
12 leds, 12 Jumper wires
One of the things I really liked about this kit is the fact that it comes with a full complement of 12 jumper wires. One of the things I found slightly frustrating with the Gertboard kit was that the leds program needs 12 wires (to drive all the leds) and the kit only supplied 10. (This applied to the original Tandy kit too – I remember suggesting 12 to Darren when I bought my first one – he obviously listened.)
What’s the best thing about it?
Obviously the layout on the Multiface is rather different. You can see that a considerable amount of effort and thought has gone into it.
I think my favourite feature is the user-friendly area for setting the buffer direction. It makes it really easy to see what’s going on.
OK, let’s talk turkey (How much does it cost?)
£26.99 GBP including VAT.
When will it be out?
Soon. Probably some time next week. (i.e. ~15th-20th April 2013) I’d better get on with those software tweaks. ;)
Here’s a photo Darren sent me of a fully assembled final production version.