how can i change ultrasonic generator from 28KHz to 25Khz?

[kareem_nabil]

Good day,

i've got this board "ultrasonic generator 28KHz 600w" from china . and also i got the ultrasonic probe but unfortunately it's 25KHz . i can't send it back to china. my question is:
how can i change the frequency output of the board so it can match?. and i left everything without change will it work normally?

 

[Aussie Susan]

Do you have the specs and schematics of the devices?
If so do they state the bandwidth of the generator and probe and do they overlap enough for your purposes?
If not then you *might* be able to pull the frequency of one of the devices but you need to check the schematics to see.
Susan

 

[dick_freebird]

Some ultrasonic transducers are highly resonant (by
element mechanical configuration, bulk or surface wave)
and part of the oscillator loop. Those would resist being
"pulled". Inspect the guts and see whether you can identify
a distinct oscillator and driver, or if it's all a tight little
loop with the transducer stuck in the middle.

The probe, maybe you can get good enough results
at -10% offset from center frequency, but you might
need to look at the response vs frequency curve and
"de-embed" that profile.

 

[betwixt]

You need to work out how the 28KHz is derived. I have never seen one of these boards but my guess would be that it comes from an MCU rather than a free running oscillator or a divider chain. You could probably change the frequency by reprogramming the MCU but it may be impossible to do that without knowing the original program loaded into it and having the tools to actually program it. Worst case, you could try just changing the quartz crystal so everything runs a little slower. The crystal is the small silver can near "Ver7.7" on the label. You want to drop the output by 25/28 = 0.8928 so if you read the frequency marked on the top and multiply it by that figure you would get the new frequency you need. Without intimate knowledge of operation, it might have other consequences, for example if it has a serial interface the data rate may also be slowed down.

Brian.