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The K1-16/16 Computer

SLOMO v1

Last updated: 2010-06-28
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The front panel is called 'SLOMO', because it provides 3 sources for slow motion / single stepping: A rotary switch for single stepping, a 1 to 100 Hz slow-motion clock and a port for a Atari ST mouse which i hope serves well for single stepping (moving it slowly) or skipping with a 'fast' clock (moving it rapidly). I was tempered to create a microcontroller-based design, which would offer more options for control. But finally i decided to stick to my initial design with 74HC circuits, to keep the design consistent. The PCB is single-sided, so i can produce it myself.

The circuit is pretty simple, but has a nice feature: It does not generate spurious pulses when you switch between clock sources. E.g. you can switch between single stepper and mouse without any unwanted pulse. The method is to convert any input clock into a short pulse when it toggles. This is done by splitting the signal, delaying one slightly by a RC delay circuit and rejoining them at an exclusive OR gate. Normally the inputs to the final mixer are all low, only when the source of the enabled clock toggles there is a short high pulse which flips the final 74HC74, used as a 1:2 divider.

The routed board:

Component placement:

My component drawing for the key switch is not correct: the solder pads are at wrong positions. I have fixed it by patching the switch, bending away the pins and soldering wires which i stick in the displaced holes. I'll have to glue the switch on the PCB or it won't stay long.

Most of the circuit worked out of the box. I just had to change the resistors and capacitor for the slomo clock, because i had bought a 10k poti where it should have been a 100k one, and on test the slomo clock did not work. Measurement of the output voltage showed that the output of the opamp toggled between 1.9 and 4.4 volt. The low voltage was not low enough for the following schmitt trigger input to toggle. Two more resistors, one in place of a wire (yeah!) shifted the output into a working range.

2009-09-12: I have tested my mental rugginess and designed the front panel in Open Office. Keyboard still intact, i'm still alive. Hah, i survived Open Office!

Material

	Name		Letzte Änderung		Länge
	Frontpanel/		2019-08-20 05:21		10
	Images/		2019-08-20 05:21		5
	case.vh		2009-11-02 16:24		3927
	SLOMO 5.3 - component placement.png size: 935 × 468		2009-09-03 21:28		39170
	SLOMO 5.4 - circuit.png size: 948 × 668		2009-09-13 09:56		118130
	SLOMO 5.4.brd		2009-09-13 14:38		46400
	SLOMO 5.4.sch		2009-09-13 14:38		85893

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