SRF01说明文档和源代码.docVIP

Ultra-Sonic Ranging Design This project started after I looked at the Polaroid Ultrasonic Ranging module. It has a number of disadvantages for use in small robots etc. The maximum range of 10.7 metre is far more than is normally required, and as a result The current consumption, at 2.5 Amps during the sonic burst is truly horrendous. The 150mA quiescent current is also far too high. The minimum range of 26cm is useless. 1-2cm is more like it. The module is quite large to fit into small systems, and It’s EXPENSIVE. Here in the UK from Maplin Electronics, the module costs GB38.00 and the transducer costs a further GB17.00. In fairness, the Polaroid module does the job it was intended to do, which requires the range, but that job is not to provide the eyes of a small robot. Here is the schematic, You can download a better quality pdf (161k) version srf1.pdf The circuit is designed to be low cost. It uses a PIC12C508 to perform the control functions and standard 40khz piezo transducers. The drive to the transmitting transducer could be simplest driven directly from the PIC. The 5v drive can give a useful range for large objects, but can be problematic detecting smaller objects. The transducer can handle 20v of drive, so I decided to get up close to this level. A MAX232 IC, usually used for RS232 communication makes and ideal driver, providing about 16v of drive. The receiver is a classic two stage op-amp circuit. The input capacitor C8 blocks some residual DC which always seems to be present. Each gain stage is set to 24 for a total gain of 576-ish. This is close the 25 maximum gain available using the LM1458. The gain bandwidth product for the LM1458 is 1Mhz. The maximum gain at 40khz is 1000000/40000 = 25. The output of the amplifier is fed into an LM311 comparator. A small amount of positive feedback provides some hysterisis to give a clean stable output. The problem of getting operation down to 1-2cm is that the receiver will pick up direct coupling from