OpenPi is a KickStarter that is to be used as an IoT ‘hub’. It is a gateway device containing a sub-1GHz transceiver and a Raspberry Pi Compute module in on a custom pcb.
The block diagram here shows what it is all about (voltage regulators etc not shown):
It is a Raspberry Pi Compute in a plastic enclosure, along with a sub-1GHz wireless transceiver module and a real time clock (RTC). It has internally-facing full-size USB sockets which are pre-populated with an 802.11 (i.e. WiFi) module, and a remote keyboard/mouse wireless dongle.
The sub-1GHz module is Ciseco’s SRF board, which is a TI CC1110 series device loaded with Ciseco software. (A sub-1GHz transceiver is a radio transmitter/receiver that operates in a band where small-neighborhood level range of communication is possible at low-to-medium bitrates; the CC1110 is an integrated circuit designed to make such communication possible).
An HDMI connector and Power are the only external connectors.
There are two USB connectors facing inwards inside the enclosure, so USB peripherals can be hidden inside, and there is no Ethernet connection.
The OpenPi has EAGLE CAD files publicly available (apart from the sub-1GHz Ciseco SRF module) which is very good news for those who wish to create or modify designs incorporating the Raspberry Pi Compute board. This is what the OpenPi looks like:
This review is based on a pre-release, and as such may not represent the final product that KS supporters receive.
The custom case has some minor quality issues. Faint tool marks/dips can be seen on sides where the mould had features on the other side, and the underside is a smooth finish rather than matt finish like the rest of the case. As mentioned the marks are minor and you'd have to look extremely closely (e.g. the photo above shows some extremely faint lines around the logo).
The top and bottom clip together (with the board screwed down inside) so is really only suitable for light home use.
The style feels unusual with no mounting holes, and as presented suits a non-visible location.
The connector panel is a third piece:
This is what it looks like from the inside:
The underside panel looks like this on the inside:
When opened, the OpenPi circuit board is found screwed into the main part of the case, using four screws, one at each corner:
The two USB devices can be seen plugged in at the right of the photo above.
Removing the USB devices is quite fiddly. There is a screw in the way, so it needs to be removed first. Here the screw hole is shown circled, and the USB devices have been removed:
The mounting holes extend through the hole and do not finish flush with the pcb. Because of this and the distortion of the fixing screw, it is difficult to remove the board.
The photo above shows that the plastic is actually inside the hole in the PCB, and then the screw fits on top.
On this unit it was difficult to pull out the OpenPi board, and one screw hole was already stripped.
A revision of the production run may alleviate this.
The board design includes some features that have been overlooked, and will cause reduced connectivity or reduced range.
There are ground planes where none should be expected.
The photo below shows a ground plane directly below the USB wireless devices.
This will either detune the antenna or prevent signal being received from that direction, with the end result being a reduced wireless range.
This is the view minus the RPI board:
The ground plane also extends to other places it shouldn’t. This is the photo of the underside of the board:
The outline above close to where the ground plane has been marked, is presumably for an XBEE module (these are wireless transceiver modules).
If one with an internal antenna is used then again there should be no ground plane here. This is described in the XBEE documentation (PDF link). (snippet below).
Perhaps the OpenPi is designed for an external antenna XBEE but there is no opening or relief for one in the case that I could find.
This version had a sub-1GHz antenna:
I understand that this antenna will not be present in the final OpenPi design, but it is still worth mentioning that this antenna at present sits directly over a ground plane too.
Ideally the PCB would not extend to the edges of the enclosure, so that there is space to place the antennae near the edges. Otherwise, performance may be compromised and the antenna cable (see photo below) could be physically crushed/damaged because of the board mount design.
Sub-1GHz is a great resource, and it is a shame if range is limited due to layout. Similarly, some people may not locate their TV close to their wireless access point, and therefore 802.11 range is important to people.
There is a small wireless keyboard that is supplied with the OpenPi. It is of good quality, with clicky keys. However I believe it is not Bluetooth, but proprietary wireless. This is a shame because it cannot easily be used with other devices, without opening up the OpenPi and extracting the USB receiver unit. A Bluetooth keyboard would have had reuse with tablets too.
This is the underside of the keyboard:
Is the OpenPi board worth the money? The answer is ‘yes’, if you want a compute module development board and don’t need Ethernet, since it is cheaper than the official compute module development board. If you need Ethernet then you have no choice but to purchase the official development board.
Otherwise, I would have to say ‘I am not sure’ because it definitely feels a very “version 0.1” product (which it is). Purchasers will want wireless with good performance, and the board does need redesign to improve on this.
To summarize, the OpenPi hardware can be a good choice depending on your needs, but it won’t be for everyone. The creators have gone to a lot of effort to provide a design that people can modify to develop their own products, and this is a very good thing to see. This review did not address the software portion of the OpenPi project.