LoRaWAN for Microbit – the verdict

Many thanks to all of you who took part in our survey, it has been very helpful. Apologies to those who had problems with the survey towards the end of the week – not sure why it started playing up.

I had intended to share the survey results but “free” Survey Monkey has some limitations and annoyingly exporting the results is one of them.

Nevertheless here’s a summary. I have excluded a few responses – A.Penguin from Antartica was a favourite

, but there were one or two others that were outliers. That said if the person who wants 1,000 for €95 each is serious, please get back in touch!!

1. How many LoRaWAN shields would you be interested in ordering.
In total we had potential first orders for around 120 shields, with conditional follow on orders of about 300.

2. How much would you pay per unit?
The average min figure was €10 and the average max figure was €27. The most common max figures were €20 and €30.

3. How soon would you be placing an order?
Nearly everyone said either now or within 3 months.

4. To what country would you want them delivered?
15 in the UK, 4 in the Netherlands, 2 USA, 1 in Germany, France and (ahem) Antarctica

5. What email address… I’m not sharing email addresses – hope you agree!

So how much can we make them for?

Richard’s design has been open source from day one, so in the same spirit here is the full bill of materials for the board, along with prices for 100 units:

Device Package Description Manufacturer MPN Supplier Supplier Part No Price (£)
2AA Battery Holder Custom Battery Holder Unknown Rapid electronics 18-0561 30
CAP_CERAMIC0603 0603 Ceramic Capacitors TDK C1608C0G1H120J080AA Farnell 1907285 2.08
CAP_CERAMIC0603 0603 Ceramic Capacitors TDK C1608C0G1H100D080AA Farnell 1907284 2.1
CAP_CERAMIC0603 0603 Ceramic Capacitors TDK C1608X8R1E104K080AA Farnell 234-6915 5.46
CAP_CERAMIC0603 0603 Ceramic Capacitors Murata GRM188R60J106KE47D Farnell 249-4230 4.85
CAP_CERAMIC0603 0603 Ceramic Capacitors Murata GRM188R60J105KA01D Farnell 952-7699 1.95
CAP_CERAMIC0603 0603 Ceramic Capacitors Murata GRM188R60J106KE47D Farnell 249-4230 4.85
CAP_CERAMIC0603 0603 Ceramic Capacitors Murata GRM188R60J105KA01D Farnell 952-7699 1.95
CAP_CERAMIC0603 0603 Ceramic Capacitors TDK C1608X8R1E104K080AA Farnell 234-6915 5.46
CAP_CERAMIC0603 0603 Ceramic Capacitors Murata GRM188R60J105KA01D Farnell 952-7699 1.95
.5A SCHOTTKY DIODE SOD123 Schottky Diode ON Semi MBR0520LT Farnell 253-3224 7.86
CARDEDGE80 CARDEDGE80 BBC Micro:Bit 80 Pos .05 Connector” Unknown Cool Components 1944 100
MOSFET-P SOT23-R P-Channel Mosfet Fairchild FDN340P Farnell 671-0435 14.7
MOSFET-NREFLOW SOT23-R N-Channel Mosfet NXP BSS138 Farnell 792-0894 6.12
RESISTOR0603 0603 Resistors Vishay CRCW0603100KFKEA Farnell 1469649 1.34
RESISTOR0603 0603 Resistors Vishay CRCW0603100KFKEA Farnell 1469649 1.34
RESISTOR0603 – NOT FITTED 0603 Resistors
RESISTOR0603 0603 Resistors Vishay CRCW0603100KFKEA Farnell 1469649 1.34
GROVE-CONNECTOR-DIP-90D(4P-2.0) HW4-2.0-90D Grove Connector TAIFENG HW4-2.0-90D Seeed Studios 110990037 10
GROVE-CONNECTOR-DIP-90D(4P-2.0) HW4-2.0-90D Grove Connector TAIFENG HW4-2.0-90D Seeed Studios 110990037 10
SPST_TACT-EVQQ2 EVQ-Q2 SMT 6mm switch, EVQQ2 series Panasonic EVQQ2P03W Farnell 2460019 20.7
0868AT43A0020 0868AT43A0020 SMT 868 Antenna Johanson 0868AT43A0020E Farnell 188-5493 48.6
RADIO MODULE RN2483 Lora Transceiver Module Microchip RN2483-I/RM101 Farnell 2758492 845
INTEGRATED CIRCUIT SOIC8-N_MC Real Time Clock Microchip MCP7940N-I/SN Farnell 2361122 52
SMD-CRYSTAL-32.768kHz SMD-3.2X1.5 Crystal FC135 Epson SMD 32.768kHz Farnell 2506942 36
NYLON SCREW M3X6 4.26
NYLON NUT M3 5.8
PCB 71
Assembly 933
Assembly VAT 446
Assembly Total cost per unit £26.75

…and that’s the problem. We can just about get them made for the maximum price people want to pay.

Several people suggested Kickstarter, which will add another 10% onto the cost, although could potentially sell many more, thereby bringing the cost per unit down. However, if we were going to sell thousands of these then we would *need* to get them CE marked which would cost approx £5,000. To be clear, we *should* get them CE marked anyway, but as that would add £50 to each of the 100or so units I don’t think that is viable.

What next?

We don’t want to give up. Can you help? Do you have any clever ideas how we can reduce the build cost?

Richard has spotted that other micro:bit shields are available for around £30, so maybe we need to approach people who have greater buying power than ourselves, and encourage them to do it? Seeed does a Grove Inventor kit for $60 which looks great – maybe they could add a LoRaWAN radio as a module for their system? Kitronik also does a range of micro:bit accessories that would look better with LoRaWAN 🙂

All suggestions very welcome!

Leave a Reply

Your email address will not be published. Required fields are marked *