RC transmitter with MC68HC711


Posted on Jun 15, 2012

The first SUPERTEF version was using a 68HC11 microprocessor in extended mode i.e. with an external memory program which necessitated many integrated circuits (IC) such as the 74C138, 74C373, 68HC24 and 27C64 making the printed circuit board densely populated and prone to defects. Now, SUPERTEF 96 uses a 68HC711E9 that is to say the same basic chip but with an INTERNAL program memory operating in `mono-chip` mode without the need for all the IC's above. The coder then became ultra-simple and except for monstrous errors, cannot not function since all that is active is IN the microprocessor. The INTERNAL storage in question has a capacity of 12 Kbytes instead of the 27C64's 8 Kbytes. The program is more performant. Let us say that it was necessary all the same to add a small external memory storage to place the data for 27 possible models.


RC transmitter with  MC68HC711
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RC transmitter with  MC68HC711 - image 1
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Figure 1 shows the diagram of the analog part of the coder. You see on the left the 4 amplifiers (U3) of the sticks' voltage (v1 to v4) with adjustment of the gains using P1 to P4 and the neutral fine adjustments, using P5 through P8. The outputs (0 to +5V) P0 to P2 are sent directly to the microprocessor. On the other hand, the auxilliaries (v5, v6 and v7), the trims (TR1 to TR4) and the gas channel (v4) are multiplexed by U1 and U2 in synchrony with the signal, before being transmitted to the microprocessor (PE3 to PE7). The circuit U3 should preferably be a LM660 from NS, with an output of 0 to +5V. Under these conditions, one can make VRL=0V and VRH=+5V, (they are the levels of reference of the A/D converter of the 68HC711) which is obtained with R12 = R13 =0. However the printed circuit makes it possible still to use a MC14573 with R12 = R13 = 47 ohms and the addition of R18. The amplifier U4A leads the tension of VARICAP of the frequency synthesized HF module and thus allows an alarm if the range of authorized variation is exceeded. The amplifier U4B formats the PPM signal by giving it the amplitude of 8V DC and the tilted sides necessary to obtain a correct HF spectrum figure. Fig. 2 illustrates the superb simplicity of the coder logic: U5 and... that is all! Port E is the 8-bit A/D converter of the microprocessor. Note that with 8 bits, it is possible to define 256 levels of precision. Knowing that a servo normally...




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