|Packaged Touchololu 0.1 PCB From PCBTrain|
The PCB was designed in Eagle CAD and fabricated by PCBTrain. The PCB is a 1.4mm, double sided and through hole plated. Intended to connect to a Hitachi HD44780 compatible LCD display. Software, running on a Microchip 16F1829 micro controller, emulates the MCP23017 used in a Panelolu 2 unit and is transparent as far as the LCD display is concerned. So potentially other LCD devices could be connected. If Touchololu configuration was required on alternate devices the Touchololu firmware would need a tweak.
PCBTrain notified a shut down, after I placed the order, over the new year. Adding quite a bit of delay to the order. So rather than 15 working days, it ended up being around a month before I received the PCB. The item was shipped in plenty of packaging and sealed in a pink bubble wrap. Presumably to extend the shelf life of the PCB. A PCBTrain engineer was good enough to contact me as I omitted an Excellon 2 drill file with the PCB layout when placing the order. I tried to use a family firm local to me; however the set up costs were quite a bit higher, although in volume they would have been quite a bit cheaper.
|Touchololu Sensor Harness For Capacitive Touch Pads|
Interestingly you can order coloured ribbon cable from Farnell electronics in meter length increments. I used the coloured ribbon cable to allow me to readily identify each of the conductors.
|Touchololu Capacitive Touch Pads In Curvy Panelolu Case|
There are two unused conductors on the harness connected to zero volts. These were reserved for a possible additional connection. They were trimmed to terminate a little before the nearest connection, rather than near the IDC connector.
The harness needs to be in a stable position, routed away from potential interference such as heavy current or noisy conductors. In this instance the cable is routed behind mounting posts and a fold placed into the ribbon cable. As the Microchip mTouch software library establishes a baseline capacitance on power up. Provided a few simple precautions are followed the software will compensate for the specific routing configuration and subsequent longer term variations should contamination arise.
Prior to installing the LCD display into the case the front was covered with Kapton tape where it might touch the capacitive touch pads.
|Touchololu LCD Bezel Insulation Prevents Contact With Pads|
The surface mount components were soldered in place followed by the connectors. The unit was programmed using a PicKit 3 programmer. When the software had been validated and the voltages on the connections to the LCD verified. The PCB was soldered to PCB header pins previously soldered to the LCD display. The PCB header pins had allowed testing of prototypes as the header pins allowed the display to be directly inserted into bread board.
|Touchololu PCB Connected To LCD Display|
The PCB was positioned to allow a micro SD card to clear the front half of the case. This will allow a slot to be placed in the rear of the Curvy Panelolu case for access to a micro SD card if required. Avoiding the need to modify the top half of the case. The PCB can be supported with a printed (3D printer) support designed to match the display PCB (clearing features as required). A support will reduce the risk of 'dry joints' being formed arising from repeated pressure on the soldered joints if the card is inserted and removed frequently.
|Touchololu MCP23017 Emulator PCB Installed On Rear Of LCD|
Finally the unit was tested using an Arduino UNO. The test software is included in the LiquidTWI library. This code can be used to test a traditional Panelolu 2 unit as well.
Having tested the unit, a ribbon cable was used to connect the Touchololu to Huxley #710. The connector to Huxley #710 is two HARWIN - M20 Series 6 way connectors. These are frequently found inside personal computers. These need HARWIN - M20-1180042 - CRIMP SOCKET. I used this connector to enable me to test in stages with a prototype and accommodate issues that might have arisen in the PCB layout.
As can be seen on the video, everything worked fine.
|Touchololu PCB Mounted On Rear Of LCD Display|
|Testing Touchololu MCP23017 Emulation With Arduino|
|Touchololu circuit diagram|