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# Parallax Oscillscope Testing RC Oscillator Circuit

Posts: 1,194
edited 2017-12-15 - 01:49:58
Anybody done this successfully?

Will post little 3 combination graph with frequencies.

4mz oscillator yields 1 million instruction per second.

I think we can get by with thousands of instructions per second.

• Posts: 1,194
edited 2017-11-17 - 20:41:46
Table 2.1

Cext

Rext Equals Average Fosc @ 5V, 25°C

20 pF

3.3 k 4.973MHz 27%
5 k 3.82MHz 21%
10 k 2.22MHz 21%
100 k 262.15 kHz 31%

100 pF

3.3 k 1.63MHz 13%
5 k 1.19MHz 13%
10 k 684.64 kHz 18%
100 k 71.56 kHz 25%

300 pF

3.3 k 660 kHz 10%
5.0 k 484.1 kHz 14%
10 k 267.63 kHz 15%
160 k 29.44 kHz 19%
• Posts: 1,194

The graph lost it's formatting copy and pasting it.

You use a 20, 100 or 300pF capacitors with one of four resistor values.

Graph shows what frequencies they will yield.

Will report on some of the results.

Need to find out what type of capacitors to use first.
• Posts: 6,156
edited 2017-11-17 - 22:10:12
Keep in mind that the Stamp boot-loader code is written for the standard resonator. You can change that, but only after programming.

A long time ago, Scott Edwards built a little BS1 board that had 4- and 8MHz (I think, could have been 16) resonators with a jumper for selecting which would be used. There are practical problems because the code for the BS1 was designed for 4MHz; debugging to the PC must be done at these speed. Once a program was debugged, though, you could change the jumper and get 2x or 4x speed -- you just had to account for this in your program.

For example
```  PAUSE 100
```
would only create a delay of 25ms if a 16MHz resonator was connected.

This is one of those things Chip "fixed" in the Propeller; the download process doesn't use the crystal (if connected) speed or PLL; downloading is done using an internal RC oscillator circuit.
Jon McPhalen
Hollywood, CA
It's Jon or JonnyMac -- please do not call me Jonny.
• Posts: 1,194
edited 2017-11-18 - 00:19:25
Jon

That's a coincidence you mentioning 8, 12 and 16 Mhz osillators.

Those are on our list. Plus a 20 Mhz to really hotrod the little chip.

Those are the ones Futurlec carries. We had to settle for a 3. something this order. No 4 Mhz.

Those are oscillators in a can. 4 lead.

Here is formula for RC circuit.

https://en.wikipedia.org/wiki/RC_time_constant

I will get the TI 83 Silver out and do one calculation.

Then guesstimate the rest.
• Posts: 1,194
edited 2017-12-15 - 01:51:02