Clock, Step and Hold logic

Preamble

Following on from Sequence Dancing – Schmitt_trigger_NAND_implementation, and the number of issues with that schematic (from CMOS 4017 Based 8 Step Sequencer)…

clk_input

Basically, the HOLD function of the schematic above does not work:

  1. An inverted (inverted by the HOLD circuit debouncing Schmitt trigger – see below) active low button press to the HOLD control (i,e, where the input to the circuit above is active high),  does not hold, but, rather, enables the clock. The active low HOLD button press is inverted by the Schmitt trigger NAND gate (see schematic below), providing an active high HOLD input to the schematic above. However, this actually enables the clock, rather than holding it.
  2. A positive edge is created when the HOLD is released, thereby advancing the clock asynchronously
  3. If the active low button press is passed through an additional inverter, so that the input to the circuit above is now active low, then the action of pressing hold gives a rising edge clock, thereby holding on the subsequent step, rather than the current step..

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Fishing with magnets

Preamble

After having seen some people doing this in the canals around Leicester and having read this article on the BBC news, The hidden dangers of magnet fishing, I thought I’d look into it.

There are a range of magnet sizes/strengths to choose from, with cost obviously increasing with strength, so which one do you need?

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