Another pest device needed

[MrDEB]

Even bought some better tweeters that have a data sheet
PSN1167 - 400 Watt 3.5'' Dispersion Horn Piezo Tweeter Pyleaudio.com ::: Your source for Car Audio, Mobile Video, Neon Lighting
Amazon.com: Pyramid TW125 7" x 3" 200 Watts Piezo Horn Tweeter: Electronics

 

[audioguru]

Am still concerned about one transistor getting very warm

It probably has low gain. Simply replace it and hope that the new one has higher gain.

would the Mosfet circuit you posted prevent any chance of heating of components?

The Mosfet turns on completely with almost no voltage across it so it won't get warm.

Even bought some better tweeters that have a data sheet

I did not see any datasheet, just a details sheet that is missing the important details. One has a manual but its link does not work.
The details claim a "frequency response" but are missing a graph and how many dB the response varies over the claimed range.
One says its capacitance is either 0.12uf or 12uf.

 

[MrDEB]

The mosfet circuit SHOULD perform as well as the transistors?
hopefully then no worry about HEAT!
will plow through the mouser catalog for some lower priced as the ones that were showen on the schematic were something like 100v?
I need to get PAINT back up and running

 

[MrDEB]

Well I decided to go with the Mosfet amp as it won't get HOT as the transistor version, depending on the gain of the transistor.
The posted circuit (see above as my MS paint won't save in png format only bit map? why?
The Mosfets are https://www.mouser.com/Search/ProductDetail.aspx?R=FDP55N06virtualkey51210000virtualkey512-FDP55N06
https://www.mouser.com/Search/ProductDetail.aspx?R=FQP17P10virtualkey51210000virtualkey512-FQP17P10
but if I can use a lower priced component? Found similar circuit that uses IRF6215 and IRF 540
Mouser does not seem to carry for a $$ comparision.
Just what criteria am I looking for in selecting a Mosfet?

 

[audioguru]

The current for the Mosfets is low when the load is a couple of piezo tweeters so the spec's of the Mosfets don't matter if they are power Mosfets in a TO-220 case.

 

[MrDEB]

well hopefully using the mosfet design AND smt for the resistors it won't get hot or warm?
The resistors are thick film 1/4 watt.
have a board designed that can be used for either unit (garden/automotive). Got a battery holder for 6 C cells but need to reconfigure as they won't fit into desired enclosure. Maybe instead of C cells go with 6 AA or AAA cells? The amp is only used for the automotive unit so battery consumption should be low.
Egads this design stuff gets complicated.

 

[MrDEB]

schematic of combo board

Having to etch my own boards as still hacking away at EAGLE (what a convoluted program) so all the resistors are smt.
the amp and voltage regulator are eliminated for battery operation.
D2 added for battery reversal protection.
The PIR / photo cell (Cds) eliminated for automotive use but regulator included as well as amp. Did breadboard the Cds section using ADC code.
Hopefully if this all works I can go entirely with smt .
Going to use velcro tape to mount tweeters to grill (no holes to drill and no $15+ enclosure.
the new tweeters are shorter in depth needed which works out better for enclosure for garden use.
Plan is to actually build a working prototype of both units using PCB instead of point to point.
have very little smt soldering experience so that's something new. Thinking of glueing the smt resistors then soldering?

 

[MrDEB]

got my paint working again but how to post so the schematic is larger than last post?

 

[MrDEB]

parts getting hot

still need to lower the 1 k resistors to 330 but concerned still about getting hot?
found several similar circuits that show a diode from the mosfet source to ground.
wonder if this might help?


**broken link removed**
Amp works great but can't have hot!
contemplating mounting mosfets on outside of enclosure and add heat sinks? but maybe getting to "overkill"
going to insert 470 ohm resistors across the 1K smd resistors and ??

 

[audioguru]

I don't see any 1k resistors. I can't find a clear image of your schematic.

 

[MrDEB]

tracked down this schematic. I am not on my computer so schematic is not readily available but this is the schematic I followed.
As per suggestion, change the 1k resistors to 330 to compensate for the capacitance of the mosfet. Have yet to do this but purchased resistors yesterday and going to try out on way home on Friday. Unless another solution is suggested?
contemplated mounting mosfets on outside w/ heat sinks-only as last resort.

https://www.electro-tech-online.com/attachments/mosfet-amp-png.42666/

 

[audioguru]

Yes, the 1k resistors will charge and discharge the high gate capacitance of the Mosfets slowly so they are all turned on (shorting the supply and getting hot) for a fairly long time every time they switch. A smaller resistor value will speed up their switching time and help to cool them.

 

[MrDEB]

hopefully enough not to worry about the heat.
I keep hearing reference to an all in one IC with H bridge built in.
don't have a clue if it would help or be a hindrance? much less to know what to look for.
maybe mounting the mosfets outside the enclosure if the resistors don't do the deed.

 

[MrDEB]

back to repelling bats

Have a request for a bat repellent device. Back to this circuit using a 9v 200 ma wall wart and Audios suggested circuit for the LM386
outputting to a piezo tweeter.
any other suggestions before I etch a circuit board?
want to add an LED to indicate when the unit is outputting ultrasonic sound every 5 minutes for 1 minute.

 

[rogs]

Why would an ultrasonic burst repel bats? They seem to be able to ignore the echolocation 'bursts' of ultrasound, transmitted by other nearby bats, without any trouble.
Why would they not also be able to ignore the ultrasound you intend to output from your piezo tweeter?

 

[MrDEB]

Presently have a unit using same circuit in operation and seems to work.
Theroy is bats use ultrasonic to locate its prey and navigate, as I understand it. Using random ultrasonic frequencies would confuse the poor bats thus leave the area.
At least that's the theory I am going by.

 

[rogs]

As you already have it working, that answers my question. Thanks.

Here in the UK, bats are a protected species, and it is quite illegal to use any device that interferes with their hunting and feeding processes. So I guess that's why I've never come across it here.

I have built several bat detectors over the years, and find it interesting to monitor and record their ultrasonic echolocation calls. The reason I suggested that additional ultrasound might not affect them is because I have always been amazed that they appear to be able to navigate - and hunt - using ultrasound in the presence of loads of other bats doing to same thing. And they appear to be able to ignore all 'received' ultrasound apart from their own.
Still, if you have enough 'noise' interference from an external source, I guess it could confuse them. And your experiments seem to confirm that is the case.

 

[MrDEB]

The jury is still out BUT in 30 days (I offered the person buying my device a 30 day money back guarantee) I hope to have more evidence weaher it works or not for sure.
Most of the similar devices I have seen utilize a 555 chip thus only one frequiency. Have seen one circuit that uses a shift regeister for multiple frequencies but not random.
I am looking into a better output device. Presently using a piezo tweeter that only goes up to 30khz.