2 layers28.3 × 39.8 mm
LevelShifter
gusmanb/logicanalyzer
24 channel, 100Msps logic analyzer hardware and software
21 parts5.1kGPL-3.0
2 layers64.8 × 55.9 mm
Killswitch
SaddlebackCollegeRobotics/killswitch_pcbHard and soft stop pcb for the rover. The PCB controls the energization of respective relay's coil.
- Size
- 64.8 × 55.9 mm
- Copper layers
- 2
- Thickness
- 1.6 mm
- Parts
- 21
- Nets
- 13
- Pads
- 47
- Tracks, vias
- 87, 7
- Routed
- Yes
- KiCad
- KiCad 5 (file 20171130)
- Created
- 29 May 2022
- Updated
- 18 Jun 2022
Overview
Killswitch is an open-source printed circuit board by SaddlebackCollegeRobotics, from the SaddlebackCollegeRobotics/killswitch_pcb repository on GitHub. It is a 2-layer board of 64.8 × 55.9 mm with 21 parts on 13 nets, routed with 87 tracks and 7 vias.
It is built around the IRFS3806TRLPBF. Its parts include 5 resistors, 5 connectors, 3 diodes and 2 ICs.
Main components
1README
README.mdKillswitch PCB
Hard and soft stop pcb for the rover. The hard stop cuts power for all subsystems. The soft stop also cuts power but it leaves computing power on. The PCB controls the energization of the Electrical (computing power), Arm, and Drive relay's coil.
The design of the PCB is recorded in osiris_meta #51.
Materials for the PCB
- General purpose diodes
- Screw terminals
48V-coil Relays12V-coil Relays500 ohm resistorno resistor for relay's coil- Coin cell battery for OR gate
- 10k pull down resistors
Cool photo of first assembly
(02.22.2022)
02/22/2022 Testing PCB
During testing (osiris_meta #67), the resistors for the coil (500 ohm, 1/4 W) smoked. Using a higher resistance (6k ohm) fixed the smoking issue, but the resistor got warm. The problem can be fixed using higher wattage resistors, but I didn't have time to get them. The resistors were used to limit the current going to the coils as a safety precaution, but the current drawn from the coil is already small, so I opted to not use a resistor and short the endings on the PCB (soldered a wire instead of a resistor).
PCB works as intended without the coil resistors! The 48-V coil relay warms after less than one minute, I read online that this is a normal behaviour of relays, but one minute is too little time.
Integration in the rover
This is the schematic of how the killswitch was connected to the protection layers already in the rover. Notice that the circuit breaker goes before the relay.
05/18/2022 More testing
The metal switch contacts of the relays melted together from overheat.
I had connected the 48V battery into the system, and not the 12V battery. After 5 minutes, I noticed the relays were hot. With the design of the killswitch, not having one battery (48 or 12) should not have been an issue. After troubleshooting, I concluded it was the relays and not the design of the PCB. Note that since the beginning, the relays were not reliable. The vendor didn't provide any datasheet and the build of the relay was not very professional. (The relays were bought from a third party in Walmart during the time when the team was discouraged from buying from Amazon).
I replaced the unreliable 48V coil relay with 12V ones that I found on Amazon.
Re-implementation in the rover
Summary of changes
- No longer using the Arm relay
- No resistor for coil, wire instead
- New relay's coil voltage is 12V
- The same 12V battery energizes all relays' coil. Relays provide isolation between the control signal and the switch contact
The changes were not made to the PCB itself due to lack of time.
A summary of all changes is in the picture:
Parts
21| Qty | Value | Footprint | References |
|---|---|---|---|
| 3 | 1N4001 | Diode_THT:D_DO-41_SOD81_P10.16mm_Horizontal | D1, D2, D3 |
| 3 | 500 | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R3, R4, R5 |
| 3 | IRFS3806TRLPBF | alexisawesome:NChan_MOSFET_IPB026N06NATMA1 | N-MOSFET1, N-MOSFET2, N-MOSFET3 |
| 3 | Screw_Terminal_01x02 | TerminalBlock:TerminalBlock_bornier-2_P5.08mm | J1, J4, J5 |
| 2 | 10K | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal | R1, R2 |
| 2 | Screw_Terminal_01x02 | alexisawesome:TerminalBlock_bornier-2_P5.08mm | J2, J3 |
| 1 | CR2032_Holder | alexisawesome:CR2032_Holder_SMD | U1 |
| 1 | HS | alexisawesome:TerminalBlock_bornier-2_P5.08mm | HardStop |
| 1 | LOGO | alexisawesome:SCRoboticsLogo | G*** |
| 1 | ORgate | alexisawesome:SN74AUP1G32DBVT_ORgate | U2 |
| 1 | SS | alexisawesome:TerminalBlock_bornier-2_P5.08mm | SoftStop |
Questions
How big is the Killswitch PCB?
It measures 64.8 × 55.9 mm and has 2 copper layers, 1.6 mm thick.
What parts does the Killswitch use?
21 parts, built around the IRFS3806TRLPBF. 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 Killswitch KiCad files?
From the SaddlebackCollegeRobotics/killswitch_pcb repository on GitHub, at the commit this page was made from: the board is killswitch.kicad_pcb. PCBKit opens the board in the browser, with nothing to install.
Can I use the Killswitch design in my own project?
Its repository states no licence, so its author keeps all rights: ask SaddlebackCollegeRobotics before reusing the design.
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