Best of luck then :)
Well, if you want a lower frequency range, specifically 10 to 100 Hz where you can measure up to 6000 RPM (so your desired 2000 RPM lies within range), use a dual 4-bit decade ripple counter. It's a chip that is used to divide the frequency of the signal by 2, 5 or 10. Adding it to the oscillating circuitry would result in the following electric diagram:
Since the chip 74HC390 doesn't exist in its current codename in our local market, the chip SN74390 is used instead (codenamed SN74390 at Katranji). They're actually identical chips: same pins, same operation and what not:
74HC390 chip:
SN74390 chip:
The "Osc" signal generated in the original oscillating circuit is now transmitted into the first CP (standing for clock pulse) pin of the 74HC390 chip (1CKA in on the SN74390 chip). The resulting signal is "Osc"/2 at terminal Q0 (i.e. 1QA on SN74390). The "Osc"/2 signal is then entered as the signal to the second CP pin (1CKB on the SN74390 chip) to obtain a signal "Osc"/10 ("Osc"/2 /5 = "Osc"/10) at pin Q3 (i.e. 1QD on chip SN74390). Pin "MR" (standing for master reset, actually pin 1CLR on SN74390) is grounded so that the chip is always enabled i.e. the chip stays operational at all times.
And as always, pin 8 i.e. GND is connected to ground voltage rail while pin 16 i.e. Vcc is connected to the Vcc voltage rail.
So you just need 1 chip to make the modifications. And use the signal "Osc"/10 (the one emitted by pin 1QD on SN74390 chip) as the trigger on the driver circuit (i.e. signal "OscIn" is no longer "Osc" but "Osc"/10).
