1 2Walkera WK-0701 transmitter is supplied with a ready to fly Walkera 3helicopters such as HM36, HM37, HM60. The walkera0701 module enables to use 4this transmitter as joystick 5 6Devel homepage and download: 7http://zub.fei.tuke.sk/walkera-wk0701/ 8 9or use cogito: 10cg-clone http://zub.fei.tuke.sk/GIT/walkera0701-joystick 11 12 13Connecting to PC: 14 15At back side of transmitter S-video connector can be found. Modulation 16pulses from processor to HF part can be found at pin 2 of this connector, 17pin 3 is GND. Between pin 3 and CPU 5k6 resistor can be found. To get 18modulation pulses to PC, signal pulses must be amplified. 19 20Cable: (walkera TX to parport) 21 22Walkera WK-0701 TX S-VIDEO connector: 23 (back side of TX) 24 __ __ S-video: canon25 25 / |_| \ pin 2 (signal) NPN parport 26 / O 4 3 O \ pin 3 (GND) LED ________________ 10 ACK 27 ( O 2 1 O ) | C 28 \ ___ / 2 ________________________|\|_____|/ 29 | [___] | |/| B |\ 30 ------- 3 __________________________________|________________ 25 GND 31 E 32 33 34I use green LED and BC109 NPN transistor. 35 36Software: 37 38Build kernel with walkera0701 module. Module walkera0701 need exclusive 39access to parport, modules like lp must be unloaded before loading 40walkera0701 module, check dmesg for error messages. Connect TX to PC by 41cable and run jstest /dev/input/js0 to see values from TX. If no value can 42be changed by TX "joystick", check output from /proc/interrupts. Value for 43(usually irq7) parport must increase if TX is on. 44 45 46 47Technical details: 48 49Driver use interrupt from parport ACK input bit to measure pulse length 50using hrtimers. 51 52Frame format: 53Based on walkera WK-0701 PCM Format description by Shaul Eizikovich. 54(downloaded from http://www.smartpropoplus.com/Docs/Walkera_Wk-0701_PCM.pdf) 55 56Signal pulses: 57 (ANALOG) 58 SYNC BIN OCT 59 +---------+ +------+ 60 | | | | 61--+ +------+ +--- 62 63Frame: 64 SYNC , BIN1, OCT1, BIN2, OCT2 ... BIN24, OCT24, BIN25, next frame SYNC .. 65 66pulse length: 67 Binary values: Analog octal values: 68 69 288 uS Binary 0 318 uS 000 70 438 uS Binary 1 398 uS 001 71 478 uS 010 72 558 uS 011 73 638 uS 100 74 1306 uS SYNC 718 uS 101 75 798 uS 110 76 878 uS 111 77 7824 bin+oct values + 1 bin value = 24*4+1 bits = 97 bits 79 80(Warning, pulses on ACK are inverted by transistor, irq is raised up on sync 81to bin change or octal value to bin change). 82 83Binary data representations: 84 85One binary and octal value can be grouped to nibble. 24 nibbles + one binary 86values can be sampled between sync pulses. 87 88Values for first four channels (analog joystick values) can be found in 89first 10 nibbles. Analog value is represented by one sign bit and 9 bit 90absolute binary value. (10 bits per channel). Next nibble is checksum for 91first ten nibbles. 92 93Next nibbles 12 .. 21 represents four channels (not all channels can be 94directly controlled from TX). Binary representations are the same as in first 95four channels. In nibbles 22 and 23 is a special magic number. Nibble 24 is 96checksum for nibbles 12..23. 97 98After last octal value for nibble 24 and next sync pulse one additional 99binary value can be sampled. This bit and magic number is not used in 100software driver. Some details about this magic numbers can be found in 101Walkera_Wk-0701_PCM.pdf. 102 103Checksum calculation: 104 105Summary of octal values in nibbles must be same as octal value in checksum 106nibble (only first 3 bits are used). Binary value for checksum nibble is 107calculated by sum of binary values in checked nibbles + sum of octal values 108in checked nibbles divided by 8. Only bit 0 of this sum is used. 109 110