KiCad design for PurpleDrop electrode board with improved heater conductance, designed for 100x74mm film carrier and 50x50mm top plate.
This project is designed with KiCad v5.1.5.
For a quick look, there is a Schematic and PCB fab drawing
Much of the board design is auto-generated by python scripts.
FootprintGenerator.ipynb generates the electrode and reservoir footprints.
They are all designed such that their origin should fall on the center of the
electrode "grid" positions. For this design, the pitch of the electrodes is
2.25mm. This script will generate a number of footprints, e.g. electrode_points_1_40deg_rl.kicad_mod.
The naming convention says that this footprint has 1 point per edge, the angle
of the points is 40 degrees, and it has points on the right and left edge (the
top and bottom are flat).
FiducialFootprintGenerator.ipynb generates a silkscreen footprint from an image file
(see TagImages directory), to put april tags
onto the board as fidicuals for image processing. Each tag has a unique ID to aid in
identifying which tag (as well as which version of electrode board) has been
detected.
LayoutGenerator.ipynb generates a layout.yaml file for this
kicad component layout plugin.
This positions the electrodes, and selects between the different edge variants (e.g. trbl, tr)
based on neighboring electrodes in the grid.
This makes the process of experimenting with different electrode footprints and layouts easier. Once the electrodes are positioned, the routing to the connectors is done manually.
| Part Number | Mfg | RefDes | Description | Qty |
|---|---|---|---|---|
| CLP-132-02-F-D-A | Samtec | J1,J2 | 64-pin connectors | 2 |
| 4929 | Keystone | H1-4 | #2-56 solderable threaded insert | 4 |
| PWR163S-25-25R0FE | Bourns | R1-4 | 25W resistor for heating | 4 |
| ZNI1000TA | Diodes Inc. | T1-4 | 1kohm RTD temperature sensor | 4 |
| S5B-PH-SM4-TB | JST | J3 | 5-pin connector for heaters | 1 |
| S8B-PH-SM4-TB | JST | J4 | 8-pin connector for RTDs | 1 |
- Shrinks width to fit reservoirs entirely under 50mmx50mm plate
- Corrects heater footprints
- Adds 2 internal layers to allow heaters to be located closer to the electrodes and to provide additional thermal paths between them
- Flips connector pin labeling to match purpledrop
- 0.062" thick: 0.032" was not rigid enough
- Increases size of fiducials to 6mm and uses a unique value for each fiducial
Initial version
Issues:
- Undersized heating resistor footprints
- Mislabeled pin numbers (they do not match the purpledrop numbering)
- Fiducials were a bit too small; they silk screen resolution did not reproduce them well and sometimes they are difficult to detect