Improving Maple Mini (part 2)

Tekwizz colleagues gave me feedback on Orone-mini, my current attempt to improve Maple-mini. They suggested that the board should focus more on being practical for people, especially relatively inexperienced makers, to assemble by hand, and less on being small. We agreed this mainly means using larger SMD parts which are easier to handle. Hence, I have made the components even larger than Orone-mini, which itself already uses much larger components than Maple-mini.

Another change to help make the board easier to assemble is using bigger pads and wider tracks. This is not about making a ‘DIY’ Printed Circuit Board (PCB), but about soldering parts onto it. I’ve recently worked with a lot of people who are beginners to soldering, and they have started with through hole parts. They are making a quite finely detailed board (not designed by me:-). This experience proved it is easy to overheat pads and tracks with a soldering iron, melting the glue, and detaching the copper from the board. This can be very awkward to fix or workaround. So the Orone-mini board has wider pads and tracks around through-hole soldered parts, increasing the area of copper, and hopefully making it more robust for people to assemble.

Increasing the size of parts means increasing from the Maple-mini’s 0402, and Orone-mini’s 0805, to 1206 size Surface Mount Devices (SMD). This means all of the Maple-mini 0402 size parts, that is 0.04 inch x 0.02 inch, or approximately 1mm x 0.5mm, are now 1206 size parts, which are 0.12″ x 0.06″, or approximately 3mm x 1.5mm. So each part increase to nine times the area of the Maple-mini part. I also increased the size of the protection diodes to twice their previous size. The transistor, regulators and Integrated Circuits (ICs) are the same as before. The transistor and small regulator are about the same size as a 1206 part, and there is no other package for either IC. The through hole parts are unchanged in size; I’ve used some of them with beginners, and they seem to be okay.

Not too surprisingly, I couldn’t fit the bigger-size components onto a Maple-mini size PCB. So the PCB has increased in size by 0.2 inches in each direction. The 0.1 inch pitch header pins are also 0.2 inches further apart, so now at 0.8 inches. It is still quite small at 2.3 inches x 1 inch. I am currently calling this ‘Orone-wide-mini’, though I quite like ‘Orone-mini-w’, or ‘Orone-mini-08’ (to identify the header spacing). Any suggestions?

Increasing the board size creates quite a lot of unused area on the bottom of the PCB, which is really the ‘Top’, because it’s the side people will see when using it. This bigger area gives more space for the ‘Top’ silkscreen, so that is slightly bigger. However, it also provided enough space to fix two other Maple-mini deficiencies; Orone-wide-mini has a ‘Power On’ LED, and a two-pin Molex socket for ‘External Power’.

The ‘External Power’ 2-pin Molex socket is on the same 0.1 inch grid as the boards main pin headers. So hopefully anyone intending to use Orone-wide-mini on their own strip-board circuits should find it practical to use 0.1 inch pin headers in the External Power holes and provide their own external power.

Finally, the component-side silk screen, which carries the names of components, has been increased in size, hopefully making it easier to use while assembling the board, and reducing the need for a separate assembly guide ‘component map’.

The header pins are as before; signal identical, and voltage identical with Maple-mini. So the existing Maple-mini-bootloader should ‘Just Work’ (TM 🙂

Here is a draft version of the ‘Orone-wide-mini’ board (or as pdf with comments Orone-wide-mini-v0Xr001):

Here is the schematic with the new additions of Power-on LED and External Power Molex socket. (or as pdf Orone-wide-mini-v0Xr001.sch):

This rework has set me back a bit, and I have been ‘under the waether’, so I now hope to have checked and uploaded the CAD in a couple of days.

Summary: Orone-wide-mini uses larger components, along with bigger tracks and pads and better compnent-side silk screen to help make it ‘hand assembly friendly’. It adds a Power-on LED, an External Power 2-pin Molex socket, and larger ‘user side’ silk screen, hopefully making it more useable. It retains Maple-mini signal and voltage compatible pin headers.

WARNING: This has not yet been made, so please do not assume it even works.

Improving Maple Mini (part 1)

This is a quick post to show my progress on making an improved STM32F board inspired by LeafLabs Maple-mini, and Siy’s mini48. I’ll explain more about the changes and rationale in a future post. WARNING: this board has not been assembled and tested. So please don’t assume it’s finished and ready to be used.

The main aim was to be bootloader and code compatible with Maple-mini. I believe that’s satisfied by retaining the same signal pins, for the same purposes. All the signals on the pins are the same signal sources with the same names and positions.

One aim was to retain pin compatibility with Maple-mini. However, as I made changes, I decided that the one of the defects of Maple-mini is the power supply. So Maple-mini’s analogue output voltage (the av+ pin) has been replaced by a connection to the higher-capacity digital power regulator. I’ll explain the detail later, but the key point is, for most uses of Maple-mini the pin-change is transparent. So I hope it is close-enough to pin compatible.

The main differences are:

• Redesign Maple-mini’s 4-layer PCB, as simpler, Double-sided PCB
• Single-sided Surface Mount Devices (SMD), for simpler DIY assembly
• Larger 0805 parts, replacing 0402 parts, easier (for me) to make
• Much higher capacity Voltage regulator, aim is full power from 9V input
• Polyfuse protecting Host’s USB-sockets power
• USB Electro-Static Discharge (ESD) protection for Host-USB socket
• More compact USB termination
• Simplified USB ‘pull-up resistor’; signals ‘USB device type change’
• Through-hole USB socket intended to be more robust than SMD socket

When I started, I didn’t expect to achieve Maple-mini’s useful 0.6″ row spacing of header pins. I was using relatively modest PCB Design Rules of 8mil track and space (about 0.2mm track & space).

Siy wrote that he’d packed an 48 pin STM32F into a 0.5″ pitch board! He is amazingly good at this stuff.  Inspired by Siy, I tried using a finer 6mil track and cleaeence (just over 0.15mm).

Here’s the PCB. The header pins are the same pitch and distance apart as Maple-mini (or as a PDF: Orone-mini-T6-v0Xr001):

Because the header pins are physically identical, and signal identical, it should ‘just plug in’ to a circuit using Maple-mini. The only change on the header pins is replacing ‘av+’ with the normal 3.3V ‘vcc’. As I wrote, I made this change to enable the board to safely run at higher input voltages (Vin) than Maple-mini. However, I would expect the change to be invisible for most users.

There are quite a lot of changes to the schematic. So here is the schematic, including some notes about changes (or as a PDF Orone-mini-T6-v0Xr001.sch):

I intend to post more explanation, and upload the Eagle CAD to github, soon. I hope this is useful to folks.

Tutorials on USB, SPI, I2C, CAN, LIN, etc.

Thanks to the Arduino, and others including Maple, lots of new users, beyond traditional developers and engineers, are using microcontrollers. Microcontrollers are mind-boggling pieces of equipment, genuinely worthy of the moniker ‘only limited by your imagination’. Many users create amazing projects using the excellent libraries and existing electronics. Some need to go further. They want to understand how to make the hardware do even more and different things.

I have always been the type of person who likes to understand how things work. I like to read manuals. Even as a child I read the manuals for my brother’s HiFi so I knew how to do make it do pretty much anything possible. I like looking at low-level code, and digesting Microcontroller manufacturers manuals. I like reading technical stuff, especially over a balmy Holiday Weekend.

I sometimes work with folks with technical backgrounds in software not hardware or low-level embedded systems who want to do more. They have all the knowledge and skills to program the hardware, but the hardware manuals are too hard a place to start. It is surprisingly rare to find good introductory material for low-level technology which is both approachable and also detailed enough to enable non-specialists to go further.

I was pleased to stumble into a set of resources for embedded systems at “EE Herald”
http://www.eeherald.com/section/design-guide/index.html

It includes a section of “On line Courses” on common embedded communication interface ‘standards’. The tutorials include USB, I2C, SPI, CAN, LIN, Serial, and RS232. Those standards are used to communicate with individual chips such as accelerometer sensors, other microcontrollers, host PCs, SD memory, Wii controllers, controllers in manufacturing plant, and parts of cars. There are also section on ‘IEEE 802’ local area and wide area networking standards.

The sections I’ve skimmed seem to have good coverage and a decent level of details. The tutorials include some helpful diagrams, which helps folks like me a lot, and are written at useful level of technical detail without going down to the manufacturer specific hardware.

For example USB is covered in
http://www.eeherald.com/section/design-guide/esmod14.html

I have only skimmed it, but it reads as good coverage of USB 2.0 from history to physical hardware, electrical levels, signalling, end-points and protocol including packet formats. It isn’t as detailed as the USB specifications, but I don’t think many people would want to start their! I like to get a good overview of the way a system works before digging into the detail, and I like to have a broad technical understanding to stitch detail into.

The USB article at EE Herald isn’t perfect. It includes a very brief overview of USB On-The-Go (OTG), but not enough to feel I could properly understand the STM32F USB OTG hardware. USB On-The-Go includes the more complex host-side of USB, so it would be impressive if they had got that too. I feel that is a minor and common weakness.

It is a readable alternative to
USB in a NutShell at http://beyondlogic.org/usbnutshell/
USB made Simple at http://www.usbmadesimple.co.uk/

These won’t replace the manufacturers manuals (e.g. ST Micros STM32F RM0008), but they cover generic technical detail, and look pretty good. I’m hoping they may be enough overview for anyone who wants to read low-level code or hardware specific manuals like STM32F RM0008 or the Atmel ATmega 48/88/168/328 manual.

I briefly looked at some other articles in the EE Herald design guides, and they are not all good quality. I felt disappointed by the ‘MEMS based motion sensing design’. It had almost no useful detail; I thought it was weak even as marketing ‘puff’. I wouldn’t feel ready to tackle a manufacturers MEMS datasheet after reading that.

EE Herald have some links to other sites, including this useful looking article on 1-Wire Interfaces from Maxim which has a lovely list of 1-Wire Application Note links at the end. Ideal Holiday Weekend reading 🙂