Hi Chris,

>I am working from Myke Predkos book, which I'm very impressed with, and
have
>decided to follow myke's advice and get a logic probe.
>
>What should I look for?.

In the previous replies, nobody mentioned features.  When I buy a logic
probe, I look for:

1.  "Normal"/"Pulse" Operation
2.  "TTL"/"CMOS" Inputs
3.  LEDs for "High", "Low" and "Pulse"
4.  Audible Output
5.  Circuit Ground (for when the probe is powered separately)

The Audible Output (high/low tones for logic levels and "clicks" for pulses)
is really useful and allows you to probe with your head down.

>Are logic probes all the same?

That's a good question.  I have never measured the input impedance to one of
mine - I presume that this is the primary parameter (other than the feature
list above).

I guess "stub length" would be a useful measurement for high frequency
circuits (but in these cases I would think that a logic analyzer or
high-speed oscilloscope would be best).

>Is there any other kit that would do the same job and other things as well?

I have owned four or five of the $20 (USD) Radio Shack model.  This one
seems reasonably rugged, easy to get on a Saturday or in the evening and has
all the features I want.

The HP Logic Dart looks interesting but is too much money for something that
I will replicate myself one day.

>What is a logic pulser?.

A circuit which will "overpower" the outputs already in the circuit and
drive its own signal onto the input to a chip.  Ideally, these devices
should be used with the driver chip removed from the circuit (I'm nervous
about back driving).

>Also I have a scope, an early Roman one I think, it is only rated at 6MHz.
Myke
>recomends in his book to have 20MHz. I would have thought that I would be
OK
>for working with 4MHz clock speeds, Is this right?. If not is there any way
I
>can scale a faster signal to show on my scope?.

As Dave Vanhorn mentioned, the rated bandwidth is the point where the
frequency response of the scope drops off drastically.  Ideally you want a
'scope where the rated bandwidth is much greater than the clock speed you
are measuring.

When I noted 20 MHz, I was thinking about a 1-4 MHz clock signal in which
the 20 MHz bandwidth would allow you to view at least the 5th harmonic of
the clock to get a reasonably good idea of what it looks like.

I have a 60 MHz Tek TDS 210 which I have been working with since they first
came out for Microcontroller and PC Interfacing projects and it has provided
me with adequate bandwidth for the signals and problems that I see.

HP has just released a two channel Scope/16 Channel Logic Analyzer that
looks like it should be useful, but I found the sixteen channels to be
limiting.  I would have bought it if it had 32 (or more Logic Analyzer
channels) and now I'm lusting after a TDS3000 four channel scope.

>Thanks for any assistance.

Good luck with your projects and thanx for the kind words about the book,

myke