Single Edge Nibble Transmission is a protocol used by some automotive sensors. It relies on pre-determined "tick time", and using only one signal wire it encodes data in pulse lengths.
This project is made to run on ESP32, created in Arduino IDE. Using built-in serial monitor for communication, we can set up the program to send a single frame or to send a frame cyclically with specified pause time.
A SENT message constructed here is for example 32 bits long (eight nibbles) and consists of the following components:
- 4 bits (one nibble) of status/communication information
- 24 bits (six nibbles) of signal data
- 4 bits (one nibble) for CRC error detection
Program logic cycle:
- check if new data is available on serial interface, if it is:
- fetch data from serial interface
- parse that data into buffer
- calculate all wait times needed to send pulses for given data
- send pulses as fast as possible
- if we're in a cyclic message mode, passive wait (without delay) until another transmission is needed
- if that time is up, then no need to calculate everything again, just send the pulses as last time
Measurements from example message command using logic analyzer at 100MS/s, tick time 3us (single message):
1 6 15 14 13 12 11 10
Rise / fall time of the signal was measured at around 1us, so some error will be caused by that (using dupont wires to connect on the breadboard).
| signal | value | ticks | us expected | us measured | %error |
|---|---|---|---|---|---|
| sync pulse | 56 | 168 | 169.66 | 0.99% | |
| status | 6 | 18 | 54 | 54.09 | 0.17% |
| data 0 | 15 | 27 | 81 | 81.15 | 0.18% |
| data 1 | 14 | 26 | 78 | 77.75 | 0.32% |
| data 2 | 13 | 25 | 75 | 74.99 | 0.01% |
| data 3 | 12 | 24 | 72 | 72.25 | 0.35% |
| data 4 | 11 | 23 | 69 | 68.95 | 0.07% |
| data 5 | 10 | 22 | 66 | 66.2 | 0.30% |
| CRC | 7 | 19 | 57 | 58.49 | 2.61% |