Build a Time Marker Generator

[Giovanni28]

https://copy.com/C8EdXSOi14wPCOgU

I ask you for advice, the schematic in the figure is valid to build a Time Marker Generator? Is there an IC equivalent to the LM2240?

[Paul Price]

The very legacy LM2240 uses an R-C circuit which creates delays would can be divided down in 1 to 255 in period, the output of this chip is in the form of a square wave not a marker blip and the accuracy of the output pulse train would depend on the stability and accuracy of the RC circuit components used by the LM2240. This chip's other limitation is the binary division output giving 1-2-4-8-16..etc ratios that are not be suitable for setting 1-2-5-10-100 etc pulse delay values.

I simply use a PICC18  MCU chip to generate blips or continuous pulses by creating the most simple of program: just a few lines of code looping and counting a sequence of NOP instruction cycles between toggles of a GPIO port pin using the highly stable and accurate internal system clock frequency of 64MHz.

Any other MCU or a pre-fab Arduino setup with a small PPM tolerance crystal for a rock-solid system clock might do just as well and would be easily programmable to output the time marker pulses you want.

[Giovanni28]

Thank you very much.

[LaserSteve]

I have a simple TTL circuit at home in a book that gives the 1:2:5:10 sequence driving a DAC for scope use, I'll try to remember to scan it for you.

The 2240 is obsolete, and not fun to use..

Steve

[PaulAm]

If you want to just throw something together, get a canned crystal oscillator for 10 or 20 MHz and feed it into a series of decade counters to get the frequencies you need.  Run the output into a oneshot to get the timing pip.

Or, do it all in software with an Arduino or other small processor.  If you do that, you'll probably spend more time on the UI than anything else.