| =========================== |
| Walkera WK-0701 transmitter |
| =========================== |
| |
| Walkera WK-0701 transmitter is supplied with a ready to fly Walkera |
| helicopters such as HM36, HM37, HM60. The walkera0701 module enables to use |
| this transmitter as joystick |
| |
| Devel homepage and download: |
| http://zub.fei.tuke.sk/walkera-wk0701/ |
| |
| or use cogito: |
| cg-clone http://zub.fei.tuke.sk/GIT/walkera0701-joystick |
| |
| |
| Connecting to PC |
| ================ |
| |
| At back side of transmitter S-video connector can be found. Modulation |
| pulses from processor to HF part can be found at pin 2 of this connector, |
| pin 3 is GND. Between pin 3 and CPU 5k6 resistor can be found. To get |
| modulation pulses to PC, signal pulses must be amplified. |
| |
| Cable: (walkera TX to parport) |
| |
| Walkera WK-0701 TX S-VIDEO connector:: |
| |
| (back side of TX) |
| __ __ S-video: canon25 |
| / |_| \ pin 2 (signal) NPN parport |
| / O 4 3 O \ pin 3 (GND) LED ________________ 10 ACK |
| ( O 2 1 O ) | C |
| \ ___ / 2 ________________________|\|_____|/ |
| | [___] | |/| B |\ |
| ------- 3 __________________________________|________________ 25 GND |
| E |
| |
| I use green LED and BC109 NPN transistor. |
| |
| Software |
| ======== |
| |
| Build kernel with walkera0701 module. Module walkera0701 need exclusive |
| access to parport, modules like lp must be unloaded before loading |
| walkera0701 module, check dmesg for error messages. Connect TX to PC by |
| cable and run jstest /dev/input/js0 to see values from TX. If no value can |
| be changed by TX "joystick", check output from /proc/interrupts. Value for |
| (usually irq7) parport must increase if TX is on. |
| |
| |
| |
| Technical details |
| ================= |
| |
| Driver use interrupt from parport ACK input bit to measure pulse length |
| using hrtimers. |
| |
| Frame format: |
| Based on walkera WK-0701 PCM Format description by Shaul Eizikovich. |
| (downloaded from http://www.smartpropoplus.com/Docs/Walkera_Wk-0701_PCM.pdf) |
| |
| Signal pulses |
| ------------- |
| |
| :: |
| |
| (ANALOG) |
| SYNC BIN OCT |
| +---------+ +------+ |
| | | | | |
| --+ +------+ +--- |
| |
| Frame |
| ----- |
| |
| :: |
| |
| SYNC , BIN1, OCT1, BIN2, OCT2 ... BIN24, OCT24, BIN25, next frame SYNC .. |
| |
| pulse length |
| ------------ |
| |
| :: |
| |
| Binary values: Analog octal values: |
| |
| 288 uS Binary 0 318 uS 000 |
| 438 uS Binary 1 398 uS 001 |
| 478 uS 010 |
| 558 uS 011 |
| 638 uS 100 |
| 1306 uS SYNC 718 uS 101 |
| 798 uS 110 |
| 878 uS 111 |
| |
| 24 bin+oct values + 1 bin value = 24*4+1 bits = 97 bits |
| |
| (Warning, pulses on ACK are inverted by transistor, irq is raised up on sync |
| to bin change or octal value to bin change). |
| |
| Binary data representations |
| --------------------------- |
| |
| One binary and octal value can be grouped to nibble. 24 nibbles + one binary |
| values can be sampled between sync pulses. |
| |
| Values for first four channels (analog joystick values) can be found in |
| first 10 nibbles. Analog value is represented by one sign bit and 9 bit |
| absolute binary value. (10 bits per channel). Next nibble is checksum for |
| first ten nibbles. |
| |
| Next nibbles 12 .. 21 represents four channels (not all channels can be |
| directly controlled from TX). Binary representations are the same as in first |
| four channels. In nibbles 22 and 23 is a special magic number. Nibble 24 is |
| checksum for nibbles 12..23. |
| |
| After last octal value for nibble 24 and next sync pulse one additional |
| binary value can be sampled. This bit and magic number is not used in |
| software driver. Some details about this magic numbers can be found in |
| Walkera_Wk-0701_PCM.pdf. |
| |
| Checksum calculation |
| -------------------- |
| |
| Summary of octal values in nibbles must be same as octal value in checksum |
| nibble (only first 3 bits are used). Binary value for checksum nibble is |
| calculated by sum of binary values in checked nibbles + sum of octal values |
| in checked nibbles divided by 8. Only bit 0 of this sum is used. |
