Piezoelectric transmitter

Transmitter -

1) Power
2) Mode, wireless, wired, type, frequency....
3) Tx rate
4) Desired distance
5) Data size
6) Environmentals

danadak said:

Transmitter -

1) Power
2) Mode, wireless, wired, type, frequency....
3) Tx rate
4) Desired distance
5) Data size
6) Environmentals

Click to expand...

I'm not exactly sure of the specifications but I just need it to send a signal that can be recieved in around 1m range and that I need it to be low power (<3V)

How are you going to store energy in your 22uF cap? Right now, the charge immediately discharges through your two 1k resistors. A fully charged capacitor will discharge in under a second if you can ever get it charged with the leak you have.

And, 3v isn't a "power" unit as you stated above. Watts is power. How many watts do you need snd how long do you need the circuit to be active to make a connection and transmit some information.

ZipZapOuch said:

How are you going to store energy in your 22uF cap? Right now, the charge immediately discharges through your two 1k resistors. A fully charged capacitor will discharge in under a second if you can ever get it charged with the leak you have.

Click to expand...

The resistors should control the threshold voltage of the LTC1440. How it should work is that the capacitor won't dicharge until it charges above the threshold.

The only reason the resistors are 1k right now is because I don't know how high I want the threshold to be yet.

brimsant said:

I'm not exactly sure of the specifications but I just need it to send a signal that can be recieved in around 1m range and that I need it to be low power (<3V)

Click to expand...

Also, define "transmitter". The chip you show is an RS485 .transceiver but for wired applications.

ZipZapOuch said:

Also, define "transmitter". The chip you show is an RS485 .transceiver but for wired applications.

Click to expand...

Sorry, I should have been more specific

I plan to eventually put the device in water so right now I am looking at something like a piezoelectric transducer as a transmitter.

brimsant said:

Sorry, I should have been more specific

I plan to eventually put the device in water so right now I am looking at something like a piezoelectric transducer as a transmitter.

Click to expand...

What kind of signal do you hope to transmit? Wireless, wired and which protocol?

brimsant said:

The resistors should control the threshold voltage of the LTC1440. How it should work is that the capacitor won't dicharge until it charges above the threshold.

The only reason the resistors are 1k right now is because I don't know how high I want the threshold to be yet.

Click to expand...

1K is FAR too low a value, and as already said the capacitor will never charge up, as the 2K load across the capacitor will absorb the tiny amounts of harvested energy. 22uF also won't hold much energy at all, an issue went you want to wirelessly transmit something using it's energy.

But as with all these kinds of threads, you are far too vague about your requirements - for a start tell us EXACTLY what you're trying to do, rather than how you think it should be done.

A radio solution might be a possibility. Many coin cell type solutions on web, could
be used as a starting point. Consider putting chips to sleep to save power. Or use
otehr energy harvesting techniques.




Also consider LORA solutions, google that, lots of activity.

Regards, Dana.

Hi, so yesterday I posted this post about a project I am making and after some feedback I am a bit clearer on what I want to do.

Basically, I've currently built this piezoelectric harvester that I plan to power with this PVDF piezoelectric material. The circuit will take in the generated voltage, rectify it, and store it in a capacitor. I also have a comparator LTC1440 with a threshold of around 2.9V (adjustable) that hopefully prevents the capacitor from discharging until the voltage in it has reached the threshold (this will probably take a very long time which is fine). I have already tested a circuit with just the capacitor and it does charge albeit very slowly.

Now, what I want to do is use the harvested energy to power a ultrasonic sensor that can transmit a signal. Put together, the device should charge the capacitor to the threshold over a period of time and then discharge to the sensor which sends a ping to a reciever before repeating the process again.

Right now I just mainly want to know if this project is feasible or not, and if it is how I could go about implementing this. If it isn't feasible, would there be some alternative that could be powered?

Thanks in advance

Why do you need a new post? Keep it together. Dont split your story - edit the original or add to the thread.

Follow the positive connection of your rectified voltage to the capacitor. Then follow the SAME wire as it continues around to the 1k resistor and continue through that to the other 1k resistor and back to ground.

Your capacitor will never charge because you are discharging it to ground IMMEDIATELY. Even if the capacitor is completely charged, it will discharge to microvolts in about a second. You said in your soon-to-be-closed new thread that it takes a long time to charge a capacitor with a simple circuit that only connects to the capacitor. How do you expect to charge the capacitor if it is getting discharged QUICKLY. You need a switch to block current flow, whether the switch is a Mosfets or other transistor, a logic controlled switch or a simple relay, you need to block the flow of electrons while you are trying to charge the capacitor.

Good luck.

ZipZapOuch said:

Follow the positive connection of your rectified voltage to the capacitor. Then follow the SAME wire as it continues around to the 1k resistor and continue through that to the other 1k resistor and back to ground.

Your capacitor will never charge because you are discharging it to ground IMMEDIATELY. Even if the capacitor is completely charged, it will discharge to microvolts in about a second. You said in your soon-to-be-closed new thread that it takes a long time to charge a capacitor with a simple circuit that only connects to the capacitor. How do you expect to charge the capacitor if it is getting discharged QUICKLY. You need a switch to block current flow, whether the switch is a Mosfets or other transistor, a logic controlled switch or a simple relay, you need to block the flow of electrons while you are trying to charge the capacitor.

Good luck.

Click to expand...

Hi, thanks for the reply
I went back and realized that I kind of have no idea what I'm doing, so I decided I might as well make things simpler and use a energy harvesting IC. The IC (ltc3588) has a rectifier and a buck converter inside. I've attached the new schematic below, could you please take a look and see if it would work? The threshold of the 100uf capacitor should be 3.6V.

That chip only allows output voltages of 3.45, 4.1, 4.5 and 5v (selected by the two pin logic inputs D0, D1). But, generally, a much better chip to harvest/store the energy. Now you need a way to convert that energy into a transmission signal.

brimsant said:

The threshold of the 100uf capacitor should be 3.6V

Click to expand...

According to the LTC3588 datasheet, the PGOOD pin goes high when the output cap has charged to 92% of the selected voltage.

If you set the IC for 4.1V output, that PGOOD signal will trigger at around 3.8V, which can be used to enable the transmitter (whatever that may be).
No additional comparator needed.