In The Ever lasting Chain Of Experiments The Next Project, ultrasonics part 7Part 7

In The Ever lasting Chain Of Experiments The Next Project, ultrasonic anti-fouling for boats.

Part 7

Made a change in the circuit diagram, changed pin 16 to pin 15 on the PIC:

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this to get the comparator 2 as current sense and on its other input the PIC DAC from its Vref, so you can set the cycle by cycle current limit in software from the menu, say output power, saves resisters too.

Changed the OLED display update so it fits in the 100 ms timer tick, added some stuff, just screen layout, tested the clock accuracy overnight, good to within a few seconds (depends on PIC's internal oscillator, good enough for an hour counter. I chose days and time over 'hours' as you may want to know how many days you have been on the ocean and dividing by 24 becomes difficult with lack of sleep and food and water.. And it is good to report over the radio: been adrift for 100 days... Hours means nothing to nobody

So display now looks like this if battery is still full at the start of the journey:

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it then cycles through the frequencies.

And once the battery is flat:

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I automagically switch down OLED display contrast, as OLED then needs less power. this is an interesting thing, I measured it in the OLED +Vcc last night, and measured 6.4 mA max. Then I removed the meter and OLED kept working via it's reset line, SCL line, and SDA pullup... So its more than 6.4 mA, on an other project I measured 10 mA, but anyways for 1 Ah left in the battery it is good for a hundred hours. I could blank the display, but because of above mentioned metal state of single handed long distance sailors it is better to use big font LOW BATTERY, perhaps it will ring a bell. Maybe add a beeper? LOL

I'm optimist, and that is why I think of these things And here is the code so far:

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Note that this is GPL (license) and it is entirely possible you will be eaten by sea monsters if you use it and you do not release source, But there is a lot of stuff there that you could use to learn how to progrum.

For now, gonna do some-sing elze while waiting for the parts.

In The Ever lasting Chain Of Experiments The Next Project, ultrasonic anti-fouling for boats.

Part 10, transducers

Ultrasonic 40 kHz transducer arrived (now that is fast from China):

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(its these:

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)

Never used that stuff for tronix, so: First measurement: capacitance, one measures 76 nF, the other 96 nF or thereabout.

Curiosity test, sure if it moves when you put a voltage on it, then it should produce a voltage when you move it.

So connected one to the scope. Pushing it between your hands can create a nice sinewave up to a volt or so (more if you are strong). Say 1 Hz, so bandwidth test 1.

Rubbing the rough front surface with your fingernail shows much higher frequencies in the audio range up to several hundred mV.

Speaking into it - no go- the mass is to big for that (it weights a lot).

So we have to see 2 things separately, the electrical resonance 90 nF with the driver inductance, and the mechanical resonance of the construction of the thing itself, When pinging it with the end of an instrument screwdriver I get a damped sinewave of about 20 uS, so 50 kHz Give or take some kHz, makes it a 40 kHz transducer (own mechanical resonance). Of course any metal or object you connect it to will change its mass and resonance frequency, damp it, so indeed also from basic principals it is a wide band device, as these tests show almost all the way down to DC. Not quite DC, as the charge subsides when you leave it, given any amount of pressure on it.