Pulse generator advice

Hi everyone, I'm working on a circuit to provide a voltage pulse of variable duration in response to a rising or falling edge from a computer via a USB or serial port link. I am using this one-shot pulse to modulate a laser diode, and for the project I'm working on, I would like pulses of width about 1 ms, adjustable in something like

0.1 ms increments. Does anyone have any advice for a cheap and simple solution? I have been following chapter 8 of Horowitz and Hill, especially section 8.23, using an ICM7250 timer/counter but I can't figure out the resetting / triggering. If there is an easier way to do this or if someone can help me with what I already have, I would greatly appreciate it. Thanks!
Reply to
zaky
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Analog Devices used to sell two digitally programmable delay generators - the AD9500 and the AD9501.

You can do something similar by replacing the timing resistor on a monostable - like a 74121 - with a digitally programmable current source, which can be something like a PNP current mirror driven by a DAC, but if you knew enough to get that to work, you wouldn't be posting here.

If you don't need the laser pulse to start immediately after you get the trigger pulse - and if it is coming from a computer, this seems likely - you can probably cobble together something like the ICM7250 out of CMOS, using a 40103 programmable counter

formatting link

clocked at 10kHz to set the width. The resetting/triggering won't be any less complicated, but 40103 data sheet is fairly easy to read.

-- Bill Sloman, Nijmegen

Reply to
bill.sloman

I'd start my thinking with the USB or serial ports. One common way to implement a simple USB interface is using a USB-to-serial converter chip, but from you perspective this just says there's two ways to get a serial signal, that needs a UART with uP to understand.

Another approach would be to get a USB-to-parallel-port adapter, that would let you address the problem by using the 8 programmable bits of a parallel port. You can take three or four of these bits to address a multiplex IC, such as a '4051 or two, and select binary resistors to program a oneshot. That's be a simple linear way.

Or you could use the 8 bits digitally, e.g., to setup the '40103 divider Bill Sloman recommended. DigiKey has many types of these very useful chips in stock.

Reply to
Winfield

you can get a reasonable pulse from the serial tx you have to give it the right character and buad rate to get the pulse width, and you can fine tune it by adjusting the buad rate too.

ive done something wich used this method.

Colin =^.^=

Reply to
colin

On a sunny day (Tue, 02 Oct 2007 13:23:07 -0700) it happened zaky wrote in :

PIC microcontroller. You'd have to learn to program one.

Any other solution I can think of is hardware bloat.

Reply to
Jan Panteltje

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