Cable Tester

Peripheral circuitry

Z280 and Central Heating Controllers


	The simple example on the left was to show the concept to be used. Knocked up over the weekend, it tests an ‘S’ video 4 way minidin cable for shorts, crossovers and open circuit conductors. In addition to the 4 digit display showing the status, two LEDs are used for quick identification of a ‘Pass / Fail’ condition.


	The following selection of images show the ‘finished article’ - so to speak.


	To the left we see the finished prototype built on a standard ‘eurocard’ with two DIN 41412 connectors at the top. One is for all the inputs, with the other dedicated to outputs. The 16 character display shows operating menu instructions and other relevant information.


	The two pots near to the middle of this image are for the display adjustment, one for the viewing angle, and the other for the ‘E’ timing ‘pulse stretcher’. The latter is needed as this particular display seems to have been designed for the 63xx / 68xx families of processors.



						Here we can see a close-up of the display showing an inbuilt diagnostic routine, that checks to see that all the port inputs are working ok. Testing is achieved by taking any line low, with the corresponding number coming up on the display. Can also be useful for testing individual conductors in cable assemblies.


					Simple but essential; the power input to the board. Here we see the power socket with two smaller take-offs. Also note the green power LED, the decoupling capacitor and the diodes for transient / reverse voltage protection.

				Click here for a page of notes I made for the original ‘RAMless’ prototype cable tester for the 4 way minidin lead. One simply has to apply the observations to a basic Z80 processor schematic.


	SCHEMATIC x 3


	Click on these three links to show the ‘official’ circuit diagram for the production model as drawn on ‘Orcad’. This is the actual circuit as constructed on the blue coloured boards shown above. It may be of interest to know that the EEprom programmer shown elsewhere on this site was used to download the software into the EEprom for this project.


	Concluding ideas


	Data sheet for the LM020 display used.


	Cable tester preliminary software and operating procedures.


		Links

	http://www.hampshire-shops.co.uk