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!