2 layers50.5 × 128.5 mm
2 layers61 × 37.1 mm
Touch button tester
TimGoll/pcb_touch_test1For an upcoming project I wanted to test how to implement PCB touch pads. The easiest solution that I could find was to use the TTP223 IC. All in all the design was pretty easy and straightforward.
- Size
- 61 × 37.1 mm
- Copper layers
- 2
- Thickness
- 1.6 mm
- Parts
- 21
- Nets
- 12
- Pads
- 54
- Tracks, vias
- 57, 9
- Pours
- 2
- Routed
- Yes
- KiCad
- KiCad 5 (file 20171130)
- Created
- 11 Mar 2021
- Updated
- 5 Apr 2022
Overview
Touch button tester is an open-source printed circuit board by TimGoll, from the TimGoll/pcb_touch_test repository on GitHub. It is a 2-layer board of 61 × 37.1 mm with 21 parts on 12 nets, routed with 57 tracks and 9 vias.
It is built around the TTP223-TD. Its parts include 6 capacitors, 4 resistors, 4 diodes, 3 ICs and 1 connector.
Main components
1README
README.mdTouch Pad PCB Test
For an upcoming project I wanted to test how to implement PCB touch pads. The easiest solution that I could find was to use the TTP223 IC. All in all the design was pretty easy and straightforward.
There were mainly three things to experiment:
- does my custom touchpad footprint work?
- is the minimal spacing between the pads enough?
- what size should the capacitor be?
The first two questions could be answered easily, the last one took some further investigation. The datasheet says that the capacitor should be in the range between 0 and 50pF. Some testing reaveled that 22pF seems to be the optimum for my 1.6mm thick PCB. 0pF is way too low. It triggers a change even if my finger is still a few centimeters away from the pad. This could work as a general proximity sensor, but not as a touchpad. 50pF on the other hand was too much. You have to press quite strong with your finger in the center of the pad in order to register any contact at all.
(testing the touchpads - it works!)
Parts
21| Qty | Value | Footprint | References |
|---|---|---|---|
| 4 | 2k2 | Resistor_SMD:R_0805_2012Metric_Pad1.15x1.40mm_HandSolder | R1, R2, R3, R4 |
| 3 | 0..50p | Capacitor_SMD:C_0805_2012Metric_Pad1.15x1.40mm_HandSolder | C1, C2, C3 |
| 3 | 100n | Capacitor_SMD:C_0805_2012Metric_Pad1.15x1.40mm_HandSolder | C4, C5, C6 |
| 3 | touch_button | touch_button:touch_button | touch 1, touch 2, touch 3 |
| 3 | ttp223 | Package_TO_SOT_SMD:SOT-23-6_Handsoldering | U4, U5, U6 |
| 1 | I/O | Connector_PinHeader_2.54mm:PinHeader_1x05_P2.54mm_Vertical | J1 |
| 1 | pwr | LED_SMD:LED_0805_2012Metric_Castellated | D4 |
| 1 | t1 | LED_SMD:LED_0805_2012Metric_Castellated | D1 |
| 1 | t2 | LED_SMD:LED_0805_2012Metric_Castellated | D2 |
| 1 | t3 | LED_SMD:LED_0805_2012Metric_Castellated | D3 |
Questions
How big is the Touch button tester PCB?
It measures 61 × 37.1 mm and has 2 copper layers, 1.6 mm thick.
What parts does the Touch button tester use?
21 parts, built around the TTP223-TD. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
Where can I download the Touch button tester KiCad files?
From the TimGoll/pcb_touch_test repository on GitHub, at the commit this page was made from: the board is touch_button_tester/touch_button_tester.kicad_pcb. PCBKit opens the board in the browser, with nothing to install.
Can I use the Touch button tester design in my own project?
Its repository states no licence, so its author keeps all rights: ask TimGoll before reusing the design.
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