Electrical Switch Providing Capacitance

[Mechanic]

Hi Mario,

The way you are going about this is exactly the same way I would have!

The only thing I suggest you do is to put 100nf xr5 caps on the vdd and vss pins to ground on the 4066's.

Study the code that is in the file I pointed you to, in particular the "Main" section. This file has the timing for the sd2000 and it does work. After a while you will start to figure out what is going on in the code. Also look up the datasheet for the atmega644 and look at the instruction set so you know what each command is doing.

Cheers Mick

[mario]

Hi Mick,

I have a question regarding the oscillator: When some one uses the "Tune" knob to cancel emi, exactly what sine wave characteristics is he changing?

On the scope, the frequency remains the same. The only noticeable difference is that the sine wave shifts to the left or right. The frequency does not change, or does it? I mean, assuming a stock 1.200Mhz, does the tune knob bump up/down the frequency several Hz to acheive this shift? in other words, does turning the knob clockwise/counter clockwise shift the frequency from 1.200Mhz to between 1.190-1.210Mhz according to the limit on the knob?

Also, by "xr5" capacitors, do you mean surface mount caps like this one? I wasn't able to find "xr5" caps...

Thanks

[Mechanic]

Hi Mario,

When you tune the oscillator with the tune knob, you are adjusting the voltage applied to the three s13 diodes, which changes their capacitance. This then causes a slight change in the amount of time 1 sine wave takes to complete, so it lengthens or shortens the wave. It will not change it much as you don't need much adjustment to be able to tune out emi and also it keeps the detector running the way they intended it to be! So by changing the length of the sine wave, this also changes the frequency as in 1 second you have X amount of oscillations, in this case about 1200000 full sine wave oscillations, 1.2mhz. So the tune knob may change the frequency from say 1.199000mhz to 1.201000mhz.

Now the capacitors, x5r and x7r, not xr5!
http://au.element14.com/jsp/search/b...0001%2B1000096

Yes they are smd.

Cheers Mick