Syma Forum

I analyzed my transmitter and in following paragraphs there are results of my analysis. There is the printed circuit board in Tr-board_1.jpg, board from devices side in Tr-board_2.jpg and scheme in Syma107tr-scheme.jpg.

The core of the transmitter is micro-controller SN8P2501B. The helicopter is controlled by potentiometers VR1-VR4 that are mechanically linked to throttle stick (VR1), left/right (VR2) and forward/backward (VR3) rudders and rotation adjustment knob (VR4). The micro-controller detects the actual value of potentiometer resistance by measuring the charging time of the capacitor C2. First, the capacitor is charged through the resistor R9 due to calibration. So PIN2 is configured as an output with high level and pins PIN1, PIN3, PIN5, PIN12, PIN13 and PIN14 are configured as an input. Capacitor voltage is monitored at the input PIN3 (Schmitt trigger structure as input mode) and when it reaches 0.7Vdd, this level is recognized as logical “1”. At this moment PIN2 is reconfigured as an input, so the capacitor C2 is no longer charged. PIN3 is reconfigured as an output with low level (GND) so capacitor C2 is rapidly discharged through resistor R8. After cca 1.5ms PIN1 is configured as an output with high level, PIN3is reconfigured as an input and the charging process is repeated with potentiometer VR1. Finally, the capacitor C2 is charged through the resistor R7, most likely due to verification and some corrections. The values of charging time are converted to the resistance values for VR1-VR4. Then the control code is formed and this code is broadcasted from PIN8 through transistor Q1 and IF LED diodes D1-D3. Waveforms for PIN1, PIN2, PIN3, PIN5, PIN8, PIN12, PIN13 and PIN14 are in corresponding pictures pins_01_03.jpg - pins_01_14.jpg. Potentiometers are monitored and control code is transmitted each 180ms (see pin_01.jpg).