Water injection and racing & more

[Wouter de Waal]

Hi all

Matthew asks:

>I need a voltage controlled Pulse width modulator....
>
>I need something that will accept an input voltage between 0 and 5 V...
>and a clock pulse
>
>and depending on the input voltage, output a pulse who's width varies
>linearly...
>
>have i explained this right
>
>so say there's a clock pulse, and the input voltage is 0V, I want a puls of
>2ms to be the output....
>
>if there;s a clock pulse, and the input voltage is 5V, I want a pulse of
>6ms to be output....

Does it *have* to be clocked? For a steady frequency converter, one would
generate a 0-5V sawtooth at that frequency, and compare that to the input
voltage. Then start the output pulse when the sawtooth is at zero, and end
it when the comparator sez that the sawtooth voltage has passed the input
voltage.

If you're clocking it from the crank/cam sensor, you have to generate the
sawtooth somewhat differently. This is almost what the D-jet does. The (cam)
sensor sets a flip-flip-type circuit, which then charges up an RC
combination. But the D-jet is time based, not voltage based.

You could probably build a good one-shot linear sawtooth generator using a
binary counter and a bunch of resistors, depending on the accuracy you need.

If I was at all good with ascii-art I would have drawn a couple of pictures,
if you don't get what I'm saying, ask, and I'll provide the 1000 words
required :-)

W