Quote:
Originally Posted by imhimmelkommter
I would like to know if anyone familiar in electronics, can a 555 timer circuit be incorporated into this circuit. Replacing the RC oscillator of R1, VR1 and C5 blue square area (As seen in schematic) with a 555 timer circuit. How would I go about doing that. Thank you and clear skies, Michael
The EQ-mount I am building is nearing completion, just need to attach the stepper motors and telescope cradle to support the telescope.
|
It's very easy to do. You can buy 555 timer modules on ebay.
http://www.ebay.com/itm/2PCS-5V-12V-...item4af679cba5
Some kits come as a bare board and loose components that need to be soldered. Others are fully assembled. I prefer the unassembled so that I can swap temperature stable capacitors and resistors
Your circuit has both internal and external clock inputs at S2. Leave the timer circuit you have outlined in tact. Cut the track in your existing timer circuit and connect the clock line from the 555 board at the external terminal of S2.
If you replace the capacitor with a temperature compensated cap and replace the two timing resistors with metal film resistors (mfr) you'll get much better thermal stability. NPO/COG ceramic capacitors have excellent thermal stability.
The inboard oscillator roughly seems to be adjustable from 0.14Hz to 14.5Hz. Initially, I suggest you install a 1Mohm pot to adjust the 555 frequency. If your worm is a Byers 10" 360 tooth (hard to tell from the pic) the worm rotation is about 4 mins. Initially calibrate this by timing the revolution of a pointer attached to the stepper motor shaft. Allow for the reduction gear between stepper motor and worm. eventually, fine tune by tracking a star with an illuminated crosshair eyepiece. Adjust the speed then swap in most of the resistance value with an mfr and a small part of the value with an adjustable trimpot then repeat the calibration.
A 555 has 2 timing resistors. The combined resistance determines the frequency of the circuit, the ratio determines the duty cycle, ratio of time on to time off. In your application, the duty cycle is irrelevant. The circuit only needs to provide timing pulses. Short or long pulses are the same to this circuit.
good luck