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Old 6th September 2005, 07:17 PM   #1
Loial is offline Loial  Sweden
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Default DIY signal generator?

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.
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Old 11th September 2005, 09:46 PM   #2
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maybe you can look at the velleman kit that do it on pc.

If I remember well, it's based on uC that feeds an high-speed DAC
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Old 11th September 2005, 09:55 PM   #3
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Wouldn't this be easy to do with a totem pole buffered 555 timer?
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Old 14th September 2005, 05:18 AM   #4
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Heres the only one i found with schematics. Its kit #101
kitsrus.com
MAX038 chip is available for free as a sample from MAXIM.
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Old 14th September 2005, 10:55 AM   #5
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Quote:
Originally posted by richie00boy
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.
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Old 14th September 2005, 02:18 PM   #6
Loial is offline Loial  Sweden
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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?
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Old 14th September 2005, 02:34 PM   #7
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Quote:
Originally posted by Loial
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.

Click the image to open in full size.

Bye,
Paolo
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Old 14th September 2005, 09:16 PM   #8
Loial is offline Loial  Sweden
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I've been thinking of a PIC processor myself, but my programming skills need to be refreshed. Maybe a PIC could display duty cycle and amplitude as well? anyone know any other way to display this?
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Old 15th September 2005, 07:42 AM   #9
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Quote:
Originally posted by Loial
I've been thinking of a PIC processor myself, but my programming skills need to be refreshed. Maybe a PIC could display duty cycle and amplitude as well? anyone know any other way to display this?

I just uploaded on the PIC16F84 the software found in that page without any modification.. no PIC programming skills required.
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Old 15th September 2005, 07:51 AM   #10
pekka is offline pekka  Finland
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Quote:
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
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