Very cool circuit Richard, using the same transistor for RF transmit/receive depending on the one PIC pin. Have you actually got this to work or is it still a design idea?? -Roman Richard Prosser wrote: > > OK - Here's the circuit so far - Setup for about 22MHz as the transistor is > only a 2N2222 > > L2 and C4 basically determine the frequency, with some help from C1 & C2. > > In RX mode an approx 20kHz pulse train appears at the output with about > 2.1V to 3.0 V range. The actual pulse frequency depends on the received > feild strength in a roughly logrithmic relationship. > So, the PIC has only to count the number of pulses in a given interval - or > measure the time for a number of pulses and it should be able to figure out > if there is a signal being received (i.e. it maintains a record of the > timing under idle condition and looks for a change). > > Under TX, the PIC pin changes to output and pulls low. This changes the > bias conditions and removes the super-regen effect, turning the circuit > into an oscillator. > For short ranges, this can be sufficient (I hope) to be regarded as a > transmitter. > Modulation by manchester coding should be OK to pass data at a few > kbits/sec - depending on range etc. required. > > A small aerial connected to Q1 Collector appears to assist reception. > > Note: this circuit is copied from a working PSpice simulation. I have used > the same basic circuit but with component values altered & a better > transistor at about 70MHz but have not yet tried making 2 of them & > connecting to PICs for communication. > > One area of possible difficulty is that according to the simulation, the RX > frequency is centred at about 22MHz, while the TX frequency is about 1MHz > higher. Possibly a better transistor would reduce this effect. > > As with most minimal component circuits, there is a fair amount of > interaction between components and frequency, sensitivity etc. but it may > serve as a starting point for someone. > If anyone does play with it I'd be interested to hear of the results. > > Enjoy > > Richard P > > (See attached file: superregen.jpg) > > (See attached file: superregen.jpg) > > --------------------------------------------------------------- > > Name: superregen.jpg > Part 1.2 Type: JPEG Image (image/jpeg) > Encoding: base64 -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu