Wheel encoder
(→Emergency stop) |
(→Encoder interface) |
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but as long as both cables are the same, then it should be OK. | but as long as both cables are the same, then it should be OK. | ||
| + | |||
| + | ====Connection to Teensy==== | ||
| + | |||
| + | CLK on all ports -> 100 Ohm -> pin 14 (CLK) on Teensy | ||
| + | MISO on all ports -> 100 Ohm -> pin 8 (DIN) | ||
| + | MOSI on all ports -> 100 Ohm -> pin 7 (DOUT) | ||
| + | 3.3V on all ports to pin 3.3V on Teensy | ||
| + | Chip select: | ||
| + | Rear Right -> 100 Ohm -> pin 9 | ||
| + | Rear Left -> 100 Ohm -> pin 15 | ||
| + | Steer -> 0 Ohm -> pin 20 | ||
| + | Front Left -> 0 Ohm -> pin 21 | ||
| + | Encoder A, B | ||
| + | Rear Right -> 0 Ohm -> pin 18 (A), 17 (B) | ||
| + | Rear Left -> 0 Ohm -> pin 4 (A), 5 (B) | ||
| + | Steer -> 0 Ohm -> pin 2 (A), 3 (B) | ||
| + | Front Left -> 0 Ohm -> pin 0 (A), 1 (B) | ||
===Voltage dividers=== | ===Voltage dividers=== | ||
Revision as of 14:59, 19 June 2019
Back to TerrainHopper
Contents |
Introduction
Wheel encoders are intended on all 4 motors, replacing the brake.
Initially rear motors are mounted with encoders. The encoders are of type AS5057 12 bit magnetic encoders.
Additionally encoder A and B signals are forwarded, but not enabled.
Board
Encoder interface is I2C and interfaced using a Teensy 3.1 processor, as shown in figure 1.
Figure 1. Breadboard with Teensy 3.1 and 4 8-pin connectors to the AS5047 boards. The board also holds the needed voltage dividers for battery voltage and steering potentiometer.
FRONT-RIGHT is changed to be steering encoder (may 2019).
Encoder interface
Signal wires to encoders has a 100 Ohm serial resistor (CLK, MISO, MOSI (and CS on rear encoders))
- pin 1: CLK (green-white)
- pin 2: Chip select (green)
- pin 3: MISO (orange-white)
- pin 4: GND (blue)
- pin 5: MOSI (blue-white)
- pin 6: 3.3V (orange)
- pin 7: B quadrature signal (brown-white)
- pin 8: A quadrature signal (brown)
Wires using unshielded network cable (cat-5)
NB! some network cables have different color coding in the rj45 side of the connector. The coding above conforms to T568A, but the cables used on the terrainhopper uses T568B,
but as long as both cables are the same, then it should be OK.
Connection to Teensy
CLK on all ports -> 100 Ohm -> pin 14 (CLK) on Teensy MISO on all ports -> 100 Ohm -> pin 8 (DIN) MOSI on all ports -> 100 Ohm -> pin 7 (DOUT) 3.3V on all ports to pin 3.3V on Teensy
Chip select:
Rear Right -> 100 Ohm -> pin 9 Rear Left -> 100 Ohm -> pin 15 Steer -> 0 Ohm -> pin 20 Front Left -> 0 Ohm -> pin 21
Encoder A, B
Rear Right -> 0 Ohm -> pin 18 (A), 17 (B) Rear Left -> 0 Ohm -> pin 4 (A), 5 (B) Steer -> 0 Ohm -> pin 2 (A), 3 (B) Front Left -> 0 Ohm -> pin 0 (A), 1 (B)
Voltage dividers
The Teensy AD converter for battery voltage and steering potentiometer uses 1.2V reference. The signals therefore needs voltage dividers.
Battery
The battery voltage divider uses a 27kOhm and a 1.2kOhm, allowing up to 28.2V to be measured. (in (optional) ground connection is mounted a 100 Ohm resistor to avoid or limit any ground current). There is a filter capacitor of 390nF.
Connected to pin (23) A9 on Teensy
Steering potentiometer
The steering potentiometer is supplied from 3.3V supply (through 100 Ohm resistors). The arm is then voltage divided using a 20kOhm and 11kOhm resistors, with a filter capacitor of 330nF.
Potentiometer arm is connected to pin (19) A5 on Teensy.
Emergency stop
This is intended to inform software that emergency stop is pressed - pt. only one channel for rear emergency stop, but maybe the remote should be separate.
A voltage divider is added on the emergency line with 20kOhm and 4.7kOhm, this should give a switch voltage of about 7V - assuming supply from 24 V.
Connected to pin 22 (A8) on Teensy.
