DIY signal generator?

Loial

Member
2004-11-21 10:06 pm
Gävle
I'm looking for a schematic for a signal generator.
My requirements are:

Squarewave output, with pulse with modulation.¨
( sine not necessary, but could be useful later. )
speed up to 500kHz
fast riserates
(high current drive capabilities ( ~1A ) )

... as you've already guessed I'm going to use it to evaluate
SMPS transformers and inductances. I might solve the drive capacity by using some MOSFET drive circuits.
 
richie00boy said:
Wouldn't this be easy to do with a totem pole buffered 555 timer?

Yes, you cuold use 2 LM555s -- but a SG3524 or SG3525 for this purpose would be more helpful -- the frequency is controllable via Rt, Ct, the duty cycle is controllable via the error amplifier. Most DIYrs use these 2 chips for their attempts at switch mode power supply "creation"

btw, you can purchase a used PG501, PG502 for around $10 to $25 on EBay --

coming soon to viewers on this forum -- how to use your sound card as an impedance meter.
 

Loial

Member
2004-11-21 10:06 pm
Gävle
Yesterday I recieved 2 samples of the MAX038 circuit :)
I've also been thinking of using SG3525 or some other PWM control circuit, but the rise times aren't really impressive, I want to use this signal generator in frequencies up to 200-300 kHz, with fast rise rates. I'm not only going to use it as a device to test SMPS transformers either.

Now comes another thing to solve... It would be nice to be able to display frequency, Duty cycle, and perhaps amplitude...
Any ideas?
 
Loial said:
Yesterday I recieved 2 samples of the MAX038 circuit :)
I've also been thinking of using SG3525 or some other PWM control circuit, but the rise times aren't really impressive, I want to use this signal generator in frequencies up to 200-300 kHz, with fast rise rates. I'm not only going to use it as a device to test SMPS transformers either.

Now comes another thing to solve... It would be nice to be able to display frequency, Duty cycle, and perhaps amplitude...
Any ideas?


Hi Loial,
some times ago I builded a signal generator with the MAX038 and to display frequency I used this software loaded in a PIC16F84:

http://home.datacomm.ch/str/micro.html

(see Autoranging frequency meter). It works fine and shows frequencies from 0,9 Hz to 20 MHz! You have just to connect the input pin of the PIC (see listing for instructions) to the sync pin of the MAX038 and use a standard 16 char LCD display and it will work.
I added also some other components to improve the accuracy of the frequency computation at very low frequencies (below 2-3 kHz) but this is not strictly required.

[IMGDEAD]http://img300.imageshack.us/img300/2210/frequenz0hn.th.jpg[/IMGDEAD]

Bye,
Paolo
 
Originally posted by paologatto
I added also some other components to improve the accuracy of the frequency computation at very low frequencies (below 2-3 kHz) but this is not strictly required.

What components did you add and how big an improvement did you achieve? Could you give me a hint?

Anyways, thanks for the tip. I have been thinking about building a PIC based frequency counter for my signal generator. This seems to a a ready made solution.

Regards,
Pekka
 
EPE magazin (Everyday Practical Electronics) has published very fine project in July 2000 about Frequency Generator/Counter with LCD.

It uses MAX038 and PIC 16FXXX. They offer PCB too at a very reasonable price. I think I payed for a copy of an article and PCB something bellow 10 pounds.

It gives out sine, square and triangle. It measures ext. freq as well.

I surelly recommend this.
 
This is how I realized it. I adapted from other schematics found on the web for using components I had in stock ;)


Schematic of the Signal Generator:

[IMGDEAD]http://img375.imageshack.us/img375/9669/freqgen0cf.th.jpg[/IMGDEAD]



Schematic of the Frequency meter (using the PIC program described in previous message):

[IMGDEAD]http://img381.imageshack.us/img381/4850/freqmeter9os.th.jpg[/IMGDEAD]


Basically I added the transistor for using the MAX signal output (any waveform) as trigger signal for the freuquency counter. Initially I used the sync out of the MAX038 for triggering the PIC and worked fine, but at low frequencies the sync signal of the MAX had some noise in the raising front (don't know if my chip is damaged or is a characteristic of all chips). With the configuration in the above schematics the frequency meter is very accurate from 0,9 Hz to 10 MHz (I limited the upper bandwith to this value).

Bye,
Paolo