On this page you will find no end of interesting odds and ends, from oscillator circuitry to parallel port stuff, all of which may be used ‘as-is’ or alternatively to pattern something better or bigger!
Click here for a tried and tested transistor oscillator circuit, complete with divide by two chip and schmitt trigger gate. Note that the TTL level out from the discrete circuit is NOT exactly 50% mark to space ratio - hence the divide by two section. If, for example a 4Mhz clock is required from the Z/2 output with a 50% m-s, an 8MHz Xtal should be used.
This schematic shows a simple way of making a latched output port for any micro (except watch out for differences in the decoding lines which are shown for the Z80). I have also incorporated a ULN2803 driver chip so that bulbs / small motors / relays can be switched from it.
To the left we have a typical interface to a Digital to Analog convertor. In this case the popular MP7529 device. Use any CPU, but ignore the reference to pin 22 if using anything other than a Z80.
Click here for a typical Analog to Digital circuit using the ADC0809 chip. Please note that the EOC line is the End Of Conversion. As A-D’s of this type require a finite time to do their processing, this line signifies to the CPU that the job is done. Either ignore the line altogether (!) and allow enough time for the process to complete, poll it or use it to drive the CPU interrupt in.
The ‘preferred’ way to interface a standard Hitachi controller based LCD display to a Z80 CPU. Note that each model of CPU needs a different type of interface circuit - the Z80 being certainly one of the most difficult. The 6800 / 6502 / 6302 etc. being the easiest as they have the timing ‘E’ interface line required by the display.
An example of an eminently usable keypad circuit for that new CPU project ( I myself have used it several times, the last time on the ‘Mentor’. I even submitted it to ‘Elektor’ as it seemed to work so well. They published it without my knowledge and eventually gave me £25 for my trouble after much asking... *Wow!* I shall not describe it as the circuit is self-explanatory.
A useful information sheet on ‘why’ and ‘how to’debouncing switches.