Many devices have a USB-C connector to charge or power them. This is very convenient given the popularity of USB-C, its reversible cable design, and sturdy, compact design.
However, some devices will not draw power when using a USB-C-to-C cable connected to a spec-compliant charger, but will when using a USB-A-to-C cable. The USB-C specification requires upstream facing ports (UFPs), the port of the device receiving power, to connect pull-down resistors to the configuration channel (CC) pins. These missing pull-down resistors are a common reason why devices can draw power with A-to-C cables but not C-to-C ones.
Wouldn’t it be great to be able to add these resistors and enable USB-C-to-C power? This mod does just that. It is a small flex PCB with pads for two 5.1kohm pull-down resistors between CC1 and CC2, respectively, and GND.
This was a collaboration with Tom Hogue (tz89 from the Venture Rider forum) to translate his prototyped design onto a printed circuit board. He’s done all of the software; my contributions were entirely in hardware.
The Carb Sync Shield monitors the up to six carburetors and displays the vacuum pressure in realtime on an LCD display so the user can make adjustments to the air/fuel mix in each cylinder.
There’s an additional RPM feature that will be useful to set and monitor the idle speed on bikes that don’t have a tachometer.
The kit can be assembled by a novice using a basic soldering iron. The pressure sensors have extra-large surface mount pads and all other components are through-hole.
The shield is compatible with both the Arduino Uno v3 and the Bluetooth-capable RedBear Blend v1. It displays the RPM calculated from each of up to six simultaneous 3.3V or 5V pressure sensors on an LCD display which can be mounted directly or connected with the rainbow jumpers as shown above.
The board draws power from the carrier Uno or Blend board, which in turn can run off a 9V battery or a USB plug. The blue trim potentiometer controls the brightness of the LCD so it’s visible indoors or outdoors. The large switch sets the analog pressure sensor reference voltage to 3.3V or 5V. In the final version of the board, the switch is replaced with a 3-pin header and jumper cap.
Three digital I/O lines are broken out along with dedicated 5V or 3.3V pins to support extra sensors. It’s up to the user to match the sensor voltage on the digital line to the expected operating voltage of the Uno or Blend.
We had the boards fabricated through OSH Park, a local batch PCB service based in Oregon, and did a successful test in early November on Tom’s bike.