Function Generator

[JohnCrow]

I've just built a nice DDS Function Generator kit.
Price is under £50

http://proto-pic.co.uk/frequency-generator-kit-fg085/

Apart from the normal sine and square wave, it can also generate the following waveforms

Triangle
+ve Ramp
-ve Ramp
+ve staircase
-ve staircase

Sine is up to 200kHz, and the rest up to 10kHz
Output Amplitude 10V p-p
Although it will generate higher frequencies, they are not as pure as when below this limit.

FG085.JPG (131.81 KiB) Viewed 11691 times

Sine-FFT.jpg (39.35 KiB) Viewed 11691 times

Staircase.jpg (30.73 KiB) Viewed 11691 times

Looking at the FFT signal on the sine wave shows it generates a high purity signal
All the SMD components are pre fitted, just leaving the thro-hole components to solder

[Steve001]

What scope are you using john ? looks quite nice

steve

[JohnCrow]

Hi Steve

Its the Rigol DS1102E
I'm very impressed with it.

http://www.matrixmultimedia.com/mmforum ... 34&t=12950

The screenshots are saved to a usb thumb drive plugged in the front of the scope.

[Steve001]

Hi John,

What's it like at 45 - 65 Hz on sine wave function ?
Can you also adjust the amplitude of the wave form also ?

Steve

[JohnCrow]

Hi Steve

Amplitude can be adjusted down to 100mV

Sine purity is good even at about 50 Hz I'll do a screen grab of my scope if you want in the next day or so at 50 Hz so you can see.

For about £50 its very impressive, no problems with building as long as you have a decent magnifying glass
As I posted above, took about 1 hour to built. The SMD components are pre-fitted.
Only thing to be careful with is the push buttons are polarised internally, but can still be fitted either way round.

http://www.jyetech.com/Products/085/e08503.php

[Steve001]

Morning John,

Thanks could you check at atbout 45 Hz please ? see what it's like no rush i am away from wed till weekend

Cheers

Steve

[JohnCrow]

Hi Steve
I've attached a sample of screen dumps from the scope at 45 Hz

ScopeShots.zip

(18.47 KiB) Downloaded 447 times

[Steve001]

Thanks for that John

They look a nice crisp waveform, plastic might be getting some use now

Steve

[JohnCrow]

Hi Steve
Don't think you'll be disappointed with it if you order one.

The only niggle I had with it are the threaded standoffs that fit between the underside of the PCB and the bottom plastic base are very slightly too short.
When the bottom cover is screwed on it presses on the electrolytic capacitor on the back of PCB, causing the cover to flex slightly.

Not having any suitable longer ones in stock to replace them I used a small nut as a thick washer to extend them by about 3 mm, and used slightly longer bolts.
This could depend on the type of supplied capacitor though.