Assembling SmartMini Boards

About: I'm "sort of" retired but, like many software people, my brain refuses to switch off. So, with a couple of friends, I have set up "Quite Useful Stuff" ( - to develop quite useful things!

SmartrMini boards are great for developing Arduino Pro Mini projects and products. They come with all surface mount components pre-soldered but they require assembly of through hole components before use.

I was very nervous about soldering when I first started: "what if I overheat something?", "what if I get a blob of solder over everything?", "what if I make bad joints?" - endless "what ifs".

Soldering is a skill which is very easy to learn - infinitely easier than learning to use a wood lathe for example! A search of YouTube will reveal lots of help and the tutorials by SparkFun and Adafruit are excellent.

Tools required

  • Soldering iron. It doesn't have to be very fancy but I like the ones where you can set the temperature - such as the one shown.
  • Solder. A reel of 60:40 (60% tin, 40% lead) solder in 0.7mm diameter makes life easy. Yes, it contains lead - so work in a well ventilated environment.
  • Solder sucker. This does what it says - it sucks up solder from places where you don't want solder. It helps correct mistakes. Get a good one with a replaceable flexible nozzle and with a little stick thing to clean it out. Don't worry, you will rarely use it - honest!
  • Self closing tweezers. These are great for holding components in place while soldering the all-important first pin.
  • Precision screwdrivers.
  • Digital voltmeter.

Try ebay for all this stuff.

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Step 1: Start With the Pro Mini

Oops, I forgot, you will also need some side cutters and a small breadboard. A few spare headers, male and female, also come in handy.

The Pro Mini is a very small, very low cost and very powerful beast. Added to a SmartMini board it becomes the heart of countless projects and products. I built SmartJointer using one.

Pro Mini arrives with no legs! For use with SmartrMini you will have to solder vertical headers to the programming end (they normally come with a right-angle connector) and legs down the side.

Start with the programming end

  • Cut off a strip of 6 vertical headers.
  • Insert them, long legs down, into the breadboard.
  • Place the Pro Mini on top with the back of the board upwards.
  • Solder one pin.
  • Check that the header is hard up against the Pro Mini and not sloping. If it is not correct apply heat to the solder joint and adjust before continuing.
  • Solder the remaining pins.


It is rare to find a Pro Mini that does not work but it does happen. Better to find out now than after soldering its legs or, even worse, after soldering it to a SmartMini board!

I am assuming you know how to use the Arduini IDE to program a Pro Mini using a USB to serial module - such as the CH340G.

Connect up the programming lines as well as 5V and GND. The Pro Mini power LED should come on and the other LED may flash - many Pro Minis come with the "Blink" test code installed. You can always download the Blink sketch yourself - it comes as standard with the Arduino IDE.

You may have a faulty Pro Mini if, after double checking your wiring, the power LED does not come on.

Now for the legs

I always buy Pro Minis with the A4/A5 lines as two holes offset along one side These lines are vitally important with SmartMini because they carry the I2C signals. Some Pro Minis have these lines at one end and SmartMini has pads for adding a blob of solder to connect the correct pin to the correct signal.

  • Insert the long legs of the two 12 pin male headers into the breadboard - use the Pro Mini to check you have them spaced the correct distance apart.
  • Place the Pro Mini onto the headers with the processor upwards.
  • Solder one pin of each header.
  • Check that the headers are hard up against the Pro Mini and not sloping. If it is not correct apply heat to the solder joint and adjust before continuing.
  • Solder the remaining pins.
  • Now add a 2 pin male header to the A4/A5 holes. Solder one pin, check, adjust, solder the other pin.

I won't repeat these last instructions again but they apply to everything you solder to the SmartMini boards - solder one pin, check alignment, adjust as necessary, solder the remaining pins. Don't try to solder all pins without checking alignment - it is 100% certain you will end up with something soldered at the wrong angle.

Test again

Repeat the earlier test - just be be sure.

Step 2: Tips

The Pro Mini is normally soldered to the SmartMini HI, SA or MA boards - this makes it easy to fit a daughter board above it - at the moment SmartMini daughter boards exist for Bluetotth and WiFi.

However, some people feel more comfortable when everything is socketed. In this case you may wish to add additional female headers to take the Pro Mini - not forgetting the A4/A5 lines as shown in the first photograph.

Those with experience of soldering will have their own ways to hold components in place while soldering the first pin. Some people have asbestos fingers and just hold things in place.

Those with more sensitive fingers (like me!) can use self-closing tweezers to hold the component to the board while the first pin is soldered. Don't forget: solder one pin, check, adjust, solder the rest.

Step 3: General Assembly

The following through hole components require soldering:

  • Headers (0.1"/2.54mm spacing)
  • Electrolytic capacitors
  • Terminal blocks (SmartMini-PS, SmartMini-SA, SmartMini-MA)
  • Power jack (SmartMini-PS)
  • 5V on/off switch (SmartMini-PS)
  • LCD contrast potentiometer (SmartMini-EB)

Details of all the boards are on the Quite Useful Stuff web site and I will deal with specific boards later but we can start with the general stuff.

Each board comes with a kit of components and there are three types of headers:

  • Male single line: these are cut from the long strip using pliers.
  • Male double line: these are for the EPort connectors, Multiport connector and 5V/GND connectors.
  • Female single line: these go either side of the Pro Mini to provide easy access to all its pins. They also act as sockets for the A4988 stepper motor driver modules on the SA and MA boards.


The spacing between headers is important. For example, the PWM/digital pins (laid out so they can be used with standard RC servos) consist of 5 or 6 rows each with 3 male headers. It is not possible to align the headers the other way - this helps prevent misalignment of things like servo leads.


Electrolytic capacitors are polarised, they have a positive and negative side.

The positive side has the longer wire.

The negative side has the shorter wire and a stripe down the length of the capacitor body.

Double check before inserting each one.

Step 4: Getting Started

The 12 way female headers go either side of the Pro Mini location holes.

The 10 way double male headers are for the two EPorts, Multiport and 5V/GND lines. SmartMini-HI and SmartMini-SA have space for an 8 way 5V/GND header so this will have to be trimmed before inserting

Step 5: SmartMini-HI

The digital/PWM lines consist of six 3 way male headers.

Close to the digital/PWM ports are a 3 way male header for external RC servo power (using a standard RC servo battery and lead) and a 2 way male header for a jumper to determine if RC power is external or internal

The digital lines consist of 2 way male headers.

Step 6: SmartMini-SA and SmartMini-MA

SmartMini HI/SA/MA have a jumper which selects power for RC servo motors. With the jumper in place power is taken from the 5V digital power. With the jumper removed power must be provided by an external source connected to the three pin header which is compatible with RC servo power supplies


The jumper must be removed when using an external power supply for servos. Your Pro Mini will be destroyed if the jumper remains in place and the supply voltage is greater than 5V.

Motor drivers

The single and multi axis board require two 8 way female headers to take A4988 stepper driver modules.

Under each module there are three 2 way male headers used for jumpers to select stepper resolution (full, half, quarter, eighth and sixteenth).

One of the larger capacitors is inserted under each A4988 driver module. Bend the leads at right angles before inserting them into the board. (Check polarity: the longest wire is positive.)

Motor terminals

The green terminals used for motor connections should be fitted together before soldering in place. Look carefully at the sides of the terminals and you will see how they slide together. This is a little fiddly the first time you do it but when done properly you should hardly see the join between them.

Step 7: SmartMini-PS: Power Supply

Soldering SmartMini-PS is straightforward but make sure you fit the switch the correct way round.

One side of the switch has a vertical extruded line and this side should be towards the edge of the board - see the photos above.

Step 8: SmartMini-EB

This is my favourite board because it adds so much!

It is soldered directly to the back of a 2004 (20 character x 4 line) LCD display (accessed over I2C) , has an SD card socket (accessed over SPI), an additional 32KB of EEPROM storage (accessed over I2C) and sockets for a 4 x 4 keypad which may be connected locally (inserted directly into the EB board or via the EBX extension board) or remotely (via a micro-USB cable). The keypad, local or remote, is also accessed over I2C.

SmartMini-EB has a right-angled connector for the Multiport cable - this keeps the profile of the board as low as possible for making things such as a Remote Controller. (Tip: if you are making the Remote Controller don't fit the two pin header for D8/GND in the top left corner - again, this keeps the profile as low as possible.)


When soldering the right angled Multiport connector it is important to start with the Multiport cable plugged in - this ensures that the right angled connector has enough clearance from the PCB. The red side of the cable aligns with the white dot on the PCB - this is pin 1 of the Multiport connector.

Once the connector is in place the board can be turned over and soldered.

Step 9: Other Boards and Checking the Motor Power

The other boards are very simple and self-evident.

  • EL is the Edmundson Link or "EPort"
  • EBX is an extension to the EB keypad port - used when building a Remote Controller.
  • ME is a Multiport Extender bringing out I2C and SPI lines. It also has an AVR programming port.
  • KP is a keypad port for use when building a remote keypad.

Power warning

SmartMini-PS is linked to SmartMini-HI, SA or MA using the 10 way EPort connector

The switch on SmartMini-PS controls the 5V digital power.

Motor power is always live if the jumper is in place to select internal (12V from the jack socket) or external (up to 35V from the green terminal block.)

The simple rule is: never connect anything while power is connected.

Double check the alignment of the EPort connector - the digit "1" should be top left and all legs should be inserted correctly.

If, by accident, you misalign the EPort connector while motor power is connected you will fry your Pro Mini.

Symptoms may be failure to program, corrupt flash, corrupt EEPROM or a bang, smoke and a nasty smell!

Unsoldering and replacing the Pro Mini board is possible with great care - but it is not an easy job to do! You will probably have to replace your SmartMini board and the Pro Mini.

Make, and double check, the EPort link between SmartMini-PS and other boards before inserting the power source(s).

Checking motor power

The photos show the PS and SA boards connected with an EPort connector. 12V is supplied through the jack socket. The jumper is set to select internal power for the motor

The photo at the top shows motor voltage with the 5V switch off, the photo at the bottom shows it with the switch on.

Step 10: Getting the UMP

SmartMini-UMP, Universal Mounting Plate, is made from acrylic and accepts SmartMini-PS and one of SmartMini-HI, SA or MA.

It has mounting holes for the boards and additional holes in the corners that allow it to be fitted to things such as SmartJointer.

It keeps things tidy - and I like "tidy"!

I have made loads of things with combinations of SmartMini boards, from SmartJointer, to Bluetooth controlled rotating tables, to stepper controlled point-of-sale displays, to remote web servers, to laser and LED controllers, to .....

I hope to post further Instructables in the future but you can contact me at any time via the QUS web site.

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