Saturday, 11 August 2018

BAW!! #4 Bubble Watch Part 1 (Falling Behind)

It another week back into KiCAD but this week want to make a board using Retro Bubble Displays from HP.



These little displays are no longer made unfortunately but I have a few knocking around and really love them. They are  HP QDSP-6064 LED displays and where use in calculators around the 70's and into the early 80's. These displays really pretty and have wanted to do a project with them for long time.

So my idea is to try and do a watch, but better i want to get a modern MCU on there and have a debugging watch. something that is can use to send UART or I2C communications in a hurry.

There is one example of a bubble watch based on an the Texas Instruments MSP430, by solderbug.

I'd like something more capable than an MSP430 with an integrated RTC so i don't have to add more components than necessary. I'm looking at using on of the ST  Microelectronics STM32F030C8. I packs a lots of power with a Cortex M0 32-Bit, with lots of peripherals. I comes i'm at around the £1.50 mark which is pretty good for amount of functionality. My only concern is its size   in a 7x7 mm QPF package its going to take quite a lot of  board space.

So i don't have much room to play with if this was going to be a single sided board, I also have to give room for a power supply. I want to get away form lithium-polymer cells (LiPo). If i was to use one then I have to look at how do I protect the battery from over discharging and how do i fit in a charge circuit while not costing the earth.

I have decided to go with a more humble pair of LR44 coin cells and using a boost converter to bring the voltage up. I think i will have to do some clever sleeping with the MCU to get the best out of this, but as the boost converter will run down to 1.2V input I sound get the most out of this format. Also going to have the battery voltage monitored by the MCU so it can issue a warning to change the battery, and as it is two cells in parallel it will be possible to change 1 cell at a time.


The MCU has a an RTC that can be used to wake up from standby mode. I fact there is no reason that when the display is bing looked at that the device has to be in any run mode at all. 

This means the device and display could be drawing less than 10uA. :) (I'm this mode the device could run up to 11,000h hours).

So far at writing this I have the base power board routed and ready to go.

I unfortunately I am only just finished with routing the base/power board. I'm pretty happy with it, the LR44 cell holders are taking the majority of the board area but I have managed to find a little room for the boost converter.


My problems are to do with the display board. The number of through hole pins are making it difficult to put the board into a format that I'm happy with.

  
  I was hoping i could somehow fit the MCU directly under the display, and as yet have not room for any IO breakout to allow add on modules. 

I think my approach is to put SMT landings for the bubble displays and modify some DIP 12 sockets to be able to solder them onto the pads. I thank i'm going to take the same approach with the crystal and SWD header. 
After a very quick search it seems SMT DIP sockets are freely available. 

This is how far the project is a the writing of this blog I'm going to push ahead to try and complete it had hope that I can not fall too far behind with boards to follow. 

I think my problem is this was quiet a complex project to try and complete in a week. and with this design change its set myself back a little. What this project is teaching me is sometime a redesign is what is needed and I have to just get on with it.

I hope to follow up soon with this design finished. Please let me know what you think, any comments are always welcome thank you to everyone who has given me feedback. 

Wednesday, 1 August 2018

BAW!! #3 Into KiCAD and RabidCHARLIE

Board A Week, Week 3 Into KiCAD and RabidCHARLIE

When designing PCB's there several software packages to choose from, these can range from free Open Source options all the way up to full fledged highly integrated software suits. My normal choice for PCB design is Autodesk Eagle, the freeware version I use at home is a great tool but limited by number of layers and board size. More info in the different versions of eagle can be found here.

When starting Board A Week I said one of the things I wanted to try was to use other design tools on of the other design tools I wanted to really give some time to is KiCAD.

KiCAD is an integrated design suit with schematic editor, layout editor and 3D viewer, I have wanted to give KiCAD a try for many years but previous attempts have been unsuccessful. The unfortunate true when you have worked with a certain piece of software for years its becomes quiet difficult to learn a new way of doing things, and consequent have returned to eagle where I'm familiar.

So lets jump into it :


I started of by you throwing down a few parts into the schematic editor and trying to understand how the schematic editor relates to the layout editor using the classic 16 x 2 Character display and an ATMega32u4 MCU. I was thinking along the lines of making some kind of industrial looking watch.

I got to a point that I realised this board would be far too complex to complete before the week was up, especially as I was still getting used to how the KiCAD operates.

I have left my first design as I left it in the GitHUB Repo I don't believe i'm deleting failed attempts as they help me to learn from my mistakes.

So in the end I restarted the board and idea to something useful and simpler a board with Charlieplexed LEDs. Charlieplexing  is a method of multiplexing LEDs by using there diode properties (only allowing current to flow in one direction. This little board could be good for testing IO speed on different devices.


KiCAD  has a very particular workflow that must be adhered to when going between working with the schematic and working with the board design.

  1. Work/Create/Modify Schematic
  2. Assign Foot prints to parts
  3. Export Netlist (important this is done after assigning footprints)
  4. Open Board layout 
  5. Import Netlist (make sure the import options are set correctly whether you want to over write footprints or remove parts that have been removed from the schematic etc.)
  6. If something is wrong repeat from step 2      



The routing tools are much the same airwires are draw between connected pads and you have to connect them with wires. In KiCAD the airwires are always up to date as well, in eagle unfortunately you have to keep hitting the restnest button to get an up-to date render of the airwires which can get annoying when trying to layout the parts in a convenient way.   



The silk and artwork import tools are amazing they import as a library item making them easy to move around.

  

The Gerber export was really straight forward and had valid Gerbers at the click of a button. Then wrapped them up in a zip file and put them into the Eurocircuts board viewer. Perfect!!!

All in all really happy with using KiCAD its powerful and precise and i think there is a lot more to learn with it. Next weeks project involves making a custom part so some new skills to look at with the software.




Tuesday, 24 July 2018

BAW!! #2 TINYMCU

I have always love Micro-controllers (MCUs') I find the fascinating the idea that there is a complete computer on one thin slice of silicone, including RAM, storage and peripherals. And these device can be small super small in fact.

On MCU I have had my eye on for a while is the Atmel Attiny10. Well I'll correct myself its now the Microchip Attiny10 as Atmel where bought out by Microchip a couple of years ago.

Name
Value
Program Memory Type
Flash
Program Memory Size (KB)
1
CPU Speed (MIPS/DMIPS)
12
SRAM Bytes
32
Capture/Compare/PWM Peripherals
1 Input Capture, 1 CCP, 2PWM
Timers
1 x 16-bit
Number of Comparators
1
Temperature Range (C)
-40 to 125
Operating Voltage Range (V)
1.8 to 5.5
Pin Count
6
Source taken from Microchip.com



Though after starting this project I discovered the PIC10F320 and PIC10F322 have the same package and pint layout. Well at least for the SOT23-6 package. 



In the schematic I have decided to add as much debug/experimenting hardware as possible so to do this I have: 
  • Added a jumper to enable the pull-up resistor for the reset pin (incase i would like to use the 4th IO line)
  • Current limiting resistors on all the IO lines ( Just good practise to avoid drawing too much current from such a tiny device each IO allows a maximum of 40mA per pin)
  • Indicator LED's (so I can get instant feedback on the pin status)
  • Jumpers to enable and disable LED's ( I have made these pin jumpers so I can use the raw pins if needed for the ADC and CLK lines if needed.)
  • Programming Header (make life easy)
  • Power indicator LED (Got to make sure there is life :) )
  • No Voltage regulator ( i want to be able to set my own voltages I would love to see how the device performs at the low end of its voltage range)


Don't forget all schematics and design files can be found at https://github.com/rabid-inventor/board-a-week  


Once I started to route the traces I discovered that the board may be able to have a single sided design. 

I rotated the MCU to try an make routing easier.


It was all going so well when I got to one last airwire. BUT:

Unfortunately the board was getting messier and messier just to make it single sided (see the bottom left corner of the board), and to get any further meant making the board size bigger and routing more around the edge. I was unfortunately time to admit defeat and route the board 2 layer.

20 mins later I had it all routed.



The design is now finished and ready to be sent for production. I'm really looking forward to having this one made, and be able to see what is possible with this tiny MCU.

I have also added a CC-BY commons licence please feel free to take a look and comment. Let me know what you think.




Thursday, 19 July 2018

BAW!! #1 XOR

Hi everyone its the first week of Boards A Week and i am kind of excited to get underway.

The first board I want to make is an Exclusive OR (XOR) gate, and XOR gate is one of the basic logic blocks used in electronic design which normal comes as an IC package containing multiple gates like MC14070B. The truth table below shows how it operates.

Truth Table


Input A Input B Output C
0 0 0
1 0 1
0 1 1
1 1 0

The reasons I wanted to design this board is to help my understanding of how complementary logic works by using discreet components, so using resistors and FETs.




The full design files can be found at http://github.com/rabid-inventor/board-a-week. I have tried to include all the source material used, including the fonts I have used for creating the silk screen.  



I'm really pleased with how this little board looks and can't wait to have it made to see if my idea works. 

I can't wait to do more of these in the passive blocks in the future. 





Wednesday, 11 July 2018

Board a week !!!!!

One of the hardest things as a maker is to keep motivated to be able to push your skills forward, and being able to make all the mistakes in the world so that you can learn from them.

So to answer this never ending problem and to improve my PCB design and understanding of electronics is I will design one board a week and share it.



These are the rules I'm setting for myself.
  • For a board to be complete it has to be fully routed (which is where all the traces are liked)
  • The DRC and ERC are complete. ( these are the checking tools in PCB design software which help the PCB designer to check if the design and electrical layouts are sound)
  • Silkscreen labels complete.
  • To try some alternative CAD software instead of Autodesk Eagle which i'm reasonably used to.
  • Publish to GIT hub as Open Source Hardware 
I don't intend on having every design made of in some cases even populated but I'm going to try and choose one design from each month to send to production.

I'll be doing a blog post each week, and trying to explain some of my design decisions and some of the methods I have tried to use.

I hope you enjoy this journey with me.

Monday, 9 July 2018

New Beginnings

Well what can I say..

Long time no post doesn't really cut it so much.

But here I am again starting to get back into the swing of writing content :)

So let bring you up to date:
  • I no longer have the Shed that I made a few videos in I miss it but times have to move on.
  • I still run a PCB assembly at Pimoroni Ltd. in Sheffield which is still an amazing mix of fun, blood, sweat and tears.
  • I have really been practising coding in C, C++ and python.
  • Trying to get to grips with Bluetooth ( A big complicated beast).

New things for the future:

As normal time is never on my side . I really want to be more focused in what skills i'm improving for myself. The 2 improvements i want to make over the coming year are PCB design and embedded programming.


I have a couple of ideas to keep me motivated, I'll keep you posted.




Monday, 30 May 2016

'Circuits, Art and Hacks' My experience of Boldport Club Membership

Beer or Beautiful circuits mmmmmm........

A few moths back there was some musings going around the twitterverse from one Saar Drimer of Boldport. It went something along the lines of:

'I'm thinking of starting something but would people pay good money for beautiful circuits'

This is the though that started The Boldport Club.

Boldport is an electronics design firm headed up by Saar focused on designing boards that are both beautiful and functional some of his designs including The Seahorse, The Life Game and The Cordwood Puzzle. Saar's PCB designs are both beautiful and unique, using every layer of the PCB to give the greatest impact including designs by exposing the copper layer and using back lighting to highlight otherwise invisible design features.

The Boldport Club is a subscription service setup by Saar for people to own their own piece of these beautifully designed circuits. These subscription costs £49 for a three months that's inclusive of taxes and shipping. The circuits are combinations of solder at home kits and single beautiful boards.

My first kit arrived a week ago and I have been itching to put it together. 



The first kit is the Pease board this is a tribute to Bob Pease a renowned designer at National Semiconductors and quoted on the front of the packaging 'My favorite programming language is solder' which makes me smile every time I hear it. The circuit provided is a light intensity to frequency converter based on the LM331 which was one of the famous ICs designed by Bob Pease.

The kit is stunningly well packed in a laser cut corrugated cardboard sandwich the amount of thought that has gone into to overall out of the box experience is breathtaking. I felt guilty opening it as it would destroy the packaging.



The story continues on opening the packaging every part feels well thought through.


The surprise in this kit is you are supplied with two PCBs I'm assuming one to make and other one is to keep as a key ring.

On close inspection of the PCB there are visible SMT pads for soldering surface mount components. Well me being me decides that I'm going to make my Pease board surface mounted. Time to find that tube of solder paste.


Surface mounted components describe components that have been soldered on top of the surface of a PCB instead of 'Through hole' or PTH the component leads pass through the board and are soldered from the opposite side of the PCB. It is very possible to hand solder SMT parts to a board in fact I do it regularly with my work, but if a reflow oven is available then applying the solder paste to the pads placing the components on the paste and melting the solder in the reflow oven is far simpler.




   

I unfortunately didn't have exact values for some of the components so I had to swap some values around.

330pF  ->  220 pF Capacitor

6.81kOhm -> 5.1kOhm Resistor

also used a Fairchild BSS138 for the drive circuit and a blue 0805 ultra bright LED.

I'm not sure what sort of effect this will have on the operation of th LM331 for pouring over the datasheet these components appear to control the frequency range.


So Here I am with the component soldered down nicely. The BSS138 seemed to be the wrong package type for this landing but the connections look secure.


Woot! it works. I found with mine that there was not much difference in the LED output but the oscilloscope told a much different story.

We if I can't get it to vary the LED brightness then just maybe I can get it to sing. So using the 3 watt amp from a Pimoroni Picade PCB, I Made a singing Pease Board/Theremin. 

   




So final thoughts on the Boldport club, I am really enjoying the kits that are coming through my door each month, the give me some new outlooks into circuit design and I can't wait to see what comes next.

If you what to become a member head over to www.boldport.club.