DIODE-SWITCHED SYNTHESISER

Posted on Feb 5, 2014

My particular favourite was the MC145152-2 that could be programmed with DIP switches, a diode matrix, or even a pair of EPROM look-up tables. But sadly, those days are over. The MC145152-2 costs about US$30, if you can find a supplier. Today we need to use PIC-processors to program modern synthesiser chips, or have them permanently connected to a computer.

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Todays synthesisers are becoming more and more surface-mounted. Whatever happened to the bits that the hobbyist can actually use What I want is a synthesiser I can use. I want it accessible. I want to be able to use diodes or solder-blobs for programming. I want just "throw together" a slack-handfull of bits and make a working synthesiser, without having to take a course in yet another processor. With these thoughts in mind I devised this project. It uses three different "bog-standard" CD4000 series CMOS chips, and not the hard-to-get ones, either. Have you ever tried to find a CD4059B recently A basic CMOS synthesiser is already on my homepages, based on the CD4046B. It can work up to about 3. 5MHz, but it is only meant to demonstrate the synthesiser principles. If you add a bit more care to the filtering then there is no reason why you cannot use it for communications. But let us now re-design that project, using easy-to-get CMOS, and add dual modulus (swallow counter) operation. Too good to be true Read on. Here is the block diagram of a basic synthesiser. The "R-counter" generates the reference frequency. In the MC145152-2 you have about 3 different options. In mine you will have over 2000 different options. The reference frequency can be interpreted as the channel-spacing of the final synthesiser. The "N-counter" divides the output of the external voltage-controlled oscillator (VCO). The output of the N-counter is...

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