sixteen logic levels on a scope

When troubleshooting digital circuits it is often useful to be able to examine the logic level of a number of signals simultaneously. For example, one might wish to look at the logic state of all the pins of a dual-in-line IC. To this end there are a number of commercially available test clips, which, via rows of LEDs, indicate which pins are at logic `1`. If one has access to an oscillo-scope, a similar result can be obtained with the aid of the circuit described here.