WeatherPi Version 2 PCB Rescued

Following my disastrous testing I decided to try rescuing my WeatherPi version 2 PCB.  In summary I'd designed the PCB wrongly, and the three IC chips had the wrong connections.

Ver-2-front-breaksOn the top of the PCB I had to break 3 tracks.  I tried a mixture of tools from a drill bit, counter sinc, and eventually ended up with a scalpel blade.  Working very carefully I was able to scratch away first the green coating, then the copper track, and to be safe some of the actual board material. I was surprised how thick the copper layer was.

On the bottom of the board I had to make 6 breaks.  I'd tried to place as many tracks on the bottom side where possible so that I could see them when troubleshooting!

2015-04-15 10.52.07I carefully solder wires to the bottom of the board using the existing pins of the IC's and headers.  I had started to use one of the unused header socket pins at the top of the board but then realized it was running at 5 volts rather than 3.3 volts.  Hence why 3 wires run to one section and one to another.

I also attempted to unsolder the 40 pin header to replace with a 24 pin header but despite using a desolder iron and desolder braid, I could not release the header.  In the end I gave in and resolder it again.

Once complete I checked there were no short circuits in the design and powered it up.

The Pi powered up and could see the three IC's, and also the temperature sensor.

So the PCB version 2 has been rescued but I don't think I'll use the other 9 boards.  At this stage I think I'll work on the design and fix the issues and make another attempt at the PCB.  Meanwhile I can work on the code to make it all work.

 

 

 

 

WeatherPi Version 2 PCB arrived and assembled

2015-04-15 10.51.39The WeatherPi version 2 PCB has finally arrived from Seedstudio in Singapore.

I'm impressed with the "customer experience" from Seedstudio and they always seem to delivery 3 weeks after initial order.

10 PCB's came in at about £20.  To have these produced in the UK would have cost about £50 for the first one

The PCB was populated in height order.  Smallest components first working my way up to the tallest components :-

  • Surface mount LED's, Resisters and switches (painful when using a soldering iron)
  • Resisters
  • IC sockets
  • Jumper style headers
  • Molex style headers
  • 40 pin Header for connecting to Pi
  • Finally the Analogue and Digital IC's, plus the DS18B20 temperature sensor

I've gone ahead and assembled it and these are my initial thoughts:-

  • Needs mounting holes to match up with the A+, B+ and Pi 2.
  • Needs mounting holes on each corner
  • The I2c headers at the top of the board are the wrong way round.  All my other PCB's have the "head board" of the header inwards. I had to switch them round to match up with existing i2c devices I have
  • It was difficult to solder the 8 different 2 way headers for the analogue ports (on the left).  Much easier to solder the 8x2 headers for digital inputs and outputs

Next step will be testing and initial power on!

 

 

 

Update on Weather Pi – February (PCB Ver 2)

Testing on the Weather Pi continues.

I already have code for all the sensors apart from the Wind Direction sensor.  The direction sensor uses 8 different resistors to indicate the wind direction using only 2 wires.  Unfortunately I've had major problems calibrating it.  The code is basically the same for detecting the light level using an LDR, but I've not been able to tune it to obtain reliable results.

I've decided that the capacitor method for detecting analogue values is not reliable enough.

PCF8591I've been working on a new PCB design that will use dedicated analogue sensors.  I could have used an 8 port SPI chip but the code looked rather complex to interpret the values.  Instead I decided to use an I2C PCF8591. Unfortunately it only has 4 ports, so I'll use 2 of them.

This is the latest PCB Design.

weather-pcb-10-x-10-Ver2-0-smd-LEDs_pcb

Major changes have been made to the PCB:-

  • 40 Pin header to connect to a Raspberry Pi A+, B+ and Pi2 (Weather Pi also works with A and B models)
  • Row of breakout pins alongside the GPIO header
  • 2 additional 3.3v I2C headers points, and 2 x 5v points
  • More header points for the temperature sensors (ds18b21)
  • Sensors that work as switches will use an MCP23017 I2C chip (Rain Quantity, Wind Speed, plus the 3 switched used for monitoring)
  • Analogue Sensors will use a PCF8591P I2C chip (Light Level, Wind Direction, Rain Detector and an additional soil moisture sensor).  There's a jumper to allow either 3.3v or 5v operation.  At the time of designing this I'm unsure if it's safe to use 5 volts.
  • The 3 LED's are joined by a 4th Blue LED, and will run via the same MCP23017.  This will allow 4 additional LED's to be added at a later date.  Red - power, Orange - Linux running, Green - script running, Blue - networking working.
  • Points added to allow surface mount Switches, LED's and resistors to be used (SMD components).
  • A 16 row breadboard style prototyping area, with 3.3v and negative power rails.

The PCB has grown from 10cm x 5cm to 10cm square.  The size is required to fit the 2 analogue chips and one digital chip.  Space may be saved in future versions by using surface mount chips.

 

Weather Pi – first one now soldered

Weather-Pi-PCB-SolderedMy first Weather Pi is now soldered up. Took about 45 minutes to solder it.

For some reason the resisters I ordered from CPC seem to be smaller than what I would class as "normal" size. This caused delays in bending the legs to the correct size.

After further research I bought resisters about 3.2mm in length rather than the normal 6mm in size.  I still haven't worked out what the difference is between them.

I decided the first Weather Pi would be a low profile version, so used 90 degree Molex connectors.

The PCB includes 3 LED connection points, but decided just to solder the LED's straight to the PCB.

 

Weather Pi – PCB Design

weather-pcb-10-x-5-Ver1-2_pcbUsing the initial Proto Plate design, I was able to turn that in to a PCB layout.  Again this was done using the Open source Fritzing computer program.

It took many iterations to obtain the best layout of the board as there's no set layout required.  Initially I tried a 5cm x 5xm layout but just couldn't get it to fit.  Then a 5cm x 10cm board was tried with the Molex connectors round the edges.  Also tried a 10 x 10cm board. Finally after many days work I managed to put all the connectors down one side of a 5cm x 5cm PCB.

Using Fritzing I was able to export the design as a Gerber file.  This is an industry standard design file for producing PCB's.  I'd used SeedStudio PCB fabricators before and was happy with the quality so decided to use them again.

SeedStudio charge about $15 for 5 copies of a 5cm x 10cm design.  Delivery can be up to 6 weeks unfortunately.

It was easy to upload the Gerber PCB files to SeedStudio and the order is now in progress.

Weather Pi – Prototype

Weather-Pi-Prototype-Proto-PlateThis is the first version of my Weather Pi for the Raspberry Pi.

I've built 4 Pi setups that have included various weather monitoring hardware - light, temperature, humidity, pressure, wind speed, water detector etc. Each has been slightly different - like GPIO pins used and style of connectorss. Each has required custom software to make it run unfortunately which has meant simple things took longer. I thought it was time to make a standard platform that I could quickly build and use.

Introducing the Weather Pi prototype:-

WeatherPi-Full-Layout

 Initial Design

weather-proto-plate-4_bb
The initial design was done using an open source program called Fritzing (http://fritzing.org/home/).  Once the Adafruit extensions are installed you can design a circuit board fairly easily.  Unfortunately there isn't an Adafruit Raspberry Pi Proto plate in the library so I had to kind of make one up.  Unfortunately the Pi connector on the Pi proto plate takes up more room than my design.

I like to use Molex connectors on my project to allow sensors to be replaced easily.  Rather than having to unsolder a sensor I can just unclip it, and clip in a new one.  This has saved so much time over the years.

Using Fritzing allowed me to minimise the amount of space used on the board for future use.  Hadn't noticed I'd basically used all the GPIO's so this was fairly pointless.

The Stand (white pipe)

In the past I've built wooden frames for my projects.  This takes a bit to design, paint and maintain.  As this project could live outside, I decided to use 40mm white drain pipe and connectors.  This pipe should be joined using welding glue but I'll probably just use hot glue.

Testing

Using existing code I was able to set up the scripts quickly.

  • Get-Weather.py - gather the data from the sensors and upload to MySQL database hosted on the web.  Run via a CRON automated job every 10 minutes
  • Rain.py - this script runs continuously waiting for the rain gauge to "flip". Once it's flipped it inserts a line in to a database hosted on the web.
  • Wind.py - This script runs for 1 minute and counts the number of times the wind sensor spins. This data is uploaded to a separate table in the database.  The script then starts for the next minute and starts again.  This effectively means it's only uploading 30 times an hour given the time it takes to upload.
  • Take-Photo.py - take a photo on the Raspberry Pi Camera and upload to the web. Run via a CRON automated job every 15 minutes
  • Monitor.py - Check networking and if there is no networking, try and start it.  Also checks the Get-Weather script is running, reboots if not.

Issues

It wasn't till I tried to plug the Molex connectors in that I realised you can't put 4 connectors side by side. There just isn't room.  This meant that one of the 4   temperature sensor sockets couldn't be used.

This was the first time I've used a wind direction sensor and it turns out it's an analogue device that returns a different resistance depending where the wind direction is.  I put this through the same kind of circuitry as the Light Sensor (LDR). Unfortunately I can't get repeatable values out of this.  Will need to see how it is long term.

The Future

Next step will be to design a PCB and have it manufactured, then further testing.  I may try redesigning this to use an MCP23017 IO Expander to handel the "switch" type devices (wind speed, rain gauge, 3 push buttons) and an MCP3008 analogue to digital converter for the LDR and wind direction sensor.

Once it's all perfected I'm looking to sell kits of the main PCB.