'Dreamer1' - LoRAwan Module based on Microchip SAMR34 - Page 1
Forum section: electronics / projects

author: mrpackethead
author_rank: Super Contributor
timestamp: February 11, 2019, 11:35:24 pm
content: I’ve just finalised my ‘dreamer1’ module design and am sending it to fab today. The motivation behind this was to create a low-cost way ( compared to the Microchip Dev board ) that was easy to prototype conceptual ideas, and or make one-off widgets with. It’s not something I would contemplate making lots of devices with.The PCB is 43 x 26mm, and the two rows of headers are aligned on a .1" ( 2.54mm ) pitch so it could be plugged into a breadboard.Its designed to be powered from USB, but you can feed power to it via the header pins, or the BAT pin. It will be possible to program it using the standard ICSP programmer pins, but also via a USB bootloader. There are a reset and user button, two dip switches, and two LEDs onboard. A number of GPIO pins, Serial RX/TX and I2C are taken to the header.This is largely based on the microchip reference design, however, I have modified it to use 0402 parts as the smallest part size so it is a little more friendly for assembly. The PCB requires some micro vias and a specific stack, which does, unfortunately, drive the cost up a little, but there’s really no way around it.The design files ( Altium ) are available on GitHub. There is a pdf of the schematic as well.https://github.com/mrpackethead/dreamer1At present, I’m intending to make 10 of these and see how they go. While I do manufacture electronics, I can’t’ see this being something I’d like to make for sale, as these kinds of things are commoditized already and its a race to the bottom in pricing. If they cost 50c more than the cost of the parts, folks would complain they are too expensive. None the less they are useful to me, and if its useful to someone else then that would be good. I need to do an itemised BOM and work out exactly how much these will cost to make at 10up, and when I do, I’ll add the info to the repo. My educated guestimate is s that including PCB, it would cost around USD$300 to make 10 buying parts from Digikey / Mouser or similar and a PCB from a Chinese PCB shop. doing it at 1000up it should get down to under $10 of parts.Already have software that does some basic stuff and will let you attach to the things network.

author: kentfielddude
author_rank: Contributor
timestamp: February 12, 2019, 06:43:57 am
content: Can you post the gerbers please?

author: nano
author_rank: Contributor
timestamp: February 12, 2019, 09:06:11 am
content: Maybe it’s just the schematic symbol that’s misleading.. For me it looks like the switches RESET and SW0 are shorted to GND.I haven’t checked the PCB though.

author: cgroen
author_rank: Unknown
timestamp: February 12, 2019, 09:15:33 am
content: I think you need to turn off "Render Text with GDI+" in Preferences->Schematic->General" to get all the text to print in the PDF schematic

author: mrpackethead
author_rank: Super Contributor
timestamp: February 12, 2019, 09:48:49 am
content: Quote from: nano on February 12, 2019, 09:06:11 amTHanks, I'll fix the schematic, so its drawn correctly. It is a wrong symbol. ( this has been floating in my librarys for a long time )

author: georges80
author_rank: Frequent Contributor
timestamp: February 12, 2019, 05:07:13 pm
content: Nice project. I went the easier route and made a board that you can solder one of the RFM style modules onto.Used an STM32 64k flash part. Added a buck/boost to run off a lifepo4 and added a PWM charger for a cheap solar panel to charge the lifepo4 battery. Some basic voltage sensing and I can PWM charge the battery up. Brought out a bunch of spare gpio pins for 'come in handy' projects. Also a header for connecting one of the cheap SD card logger modules directly to the UART pins. If not logger then I can just connect the UART pins to a GPS module for instance.(Heavily) modified radiohead code for allowing units to talk to each other since I'm not after lorawan/iot usage but more standalone data comms.Anyhow, pic of board below.I think lora is quite an impressive technology for the price point. Basic test (I have many more I need to do) was 1.5km across an open field and still getting better than -80dbm rssi being reported from the sx1276 chip using low gain antenna on each end just hand held.I think my BOM is <$10 for the board (10 piece component order) and it's about $5 for the RFM module from one of the many asian vendors. Simple 2 layer board from jcpcb.cheers,george.

author: mrpackethead
author_rank: Super Contributor
timestamp: February 12, 2019, 09:40:13 pm
content: Quote from: kentfielddude on February 12, 2019, 06:43:57 amI have pushed them to the git repo now. If you are going to build a board from it, you'll need to make sure it matches the board stackup as well.Please note that this is as still untested.

author: mrpackethead
author_rank: Super Contributor
timestamp: February 12, 2019, 09:41:16 pm
content: Quote from: nano on February 12, 2019, 09:06:11 amThanks for this. I've updated the schematic and actually replaced the switches with somethign thats better placed. Now in the repo.

author: mrpackethead
author_rank: Super Contributor
timestamp: February 12, 2019, 09:50:05 pm
content: Quote from: georges80 on February 12, 2019, 05:07:13 pmWhen you are adding a RF section to another board that is quite a useful idea. Something you do need to watch however is when your RF comes off the module to your antenna. Your trace looks like it will be pretty poorly matched ( impedance wise ). At the short distance it is, it may not be an issue. but it coudl be impacting your overall output.The SAMR34 is both a micro and the radio in the same chip. My use case is a little differnet from yours, i was wanting a way to quickly add sensors on breadboard or just wired on, without the need for another PCB. I doubt I would ever use this as part of a real product ( unless it was a one or two off ).>Used an STM32 64k flash part. Added a buck/boost to run off a lifepo4 and added a PWM charger for a cheap solar panel to charge the lifepo4 battery. Some basic voltage >sensing and I can PWM charge the battery up. Brought out a bunch of spare gpio pins for 'come in handy' projects. Also a header for connecting one of the cheap SD card logger >modules directly to the UART pins. If not logger then I can just connect the UART pins to a GPS module for instance.Yeah, you've designed something for a specific usecase. I like doign that, and getting everythign on a single board, with no wires/connectors!>I think lora is quite an impressive technology for the price point. Basic test (I have many more I need to do) was 1.5km across an open field and still getting better than -80dbm >rssi being reported from the sx1276 chip using low gain antenna on each end just hand held.For point to point, lora is great, and you get to make it run faster, and dot' ahve all the MAC overhead. When you have 200 sensors ( and they only need to send a few bytes a day ) LoRaWAN is kind of appropriate. Theres no reason why this board couldnt do the same thing. .You coudl build a 500kbit point to point Serial link with it.>I think my BOM is <$10 for the board (10 piece component order) and it's about $5 for the RFM module from one of the many asian vendors. Simple 2 layer board from jcpcb.Yes, i am always quite amazed at what you get for your money now!

author: mrpackethead
author_rank: Super Contributor
timestamp: February 13, 2019, 10:50:45 pm
content: Some updates; since i did'tn quite send it to fab, before i changed my mind. :-)Modifyed buttons, added a AT608 Crypto IC, and a Bosch Air quality sensor on the I2C bus.