Question on the Plants Watering Watcher circuit
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audioguru2
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Ante,
Thanks.
Trial and error? Yes, I was surprised that the LED drive current was too high and I had to try first 10 ohms, then 22 ohms to find a suitable current-limiting resistor.
Other than that, it is all theory, I redesigned the circuit in my head and it works exactly as I said:
Do you like my Chinese-copied epoxy-fiberglass Veroboard?
Thanks.
Trial and error? Yes, I was surprised that the LED drive current was too high and I had to try first 10 ohms, then 22 ohms to find a suitable current-limiting resistor.
Other than that, it is all theory, I redesigned the circuit in my head and it works exactly as I said:
But he never replied again, so I tried it.
Do you like my Chinese-copied epoxy-fiberglass Veroboard?
Hi there Audioguru:
I was a little bit shocked by the level of controversy that my simple question started.
As a matter of fact I started to look into other circuits as this one
( as it was) had some additional problems like the 10% mark to space
ratio that polarized the probe, and the fact that I need a linear output
as the media conductivity changes.
But with the changes you suggest, including the use of the CD74BC132, I will give it a second try.
Your help has been great !!!!
Don't be surprised if I request your help once again in order to finish my project ( sorry ! )
Best regards, JLB.
I was a little bit shocked by the level of controversy that my simple question started.
As a matter of fact I started to look into other circuits as this one
( as it was) had some additional problems like the 10% mark to space
ratio that polarized the probe, and the fact that I need a linear output
as the media conductivity changes.
But with the changes you suggest, including the use of the CD74BC132, I will give it a second try.
Your help has been great !!!!
Don't be surprised if I request your help once again in order to finish my project ( sorry ! )
Best regards, JLB.
audioguru2
- Apr 6, 2004
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JLB,
Sure, we are glad to help you.
Thanks for pointing-out the errors in our original project:
1) No dimming, as was promised by the author.
2) Very dim LED.
3) Asymmetrical duty-cycle at the probes, contrary to the text.
4) No function with most original ICs at 3V or less.
Did your typing slip on the CD74HC132?
Sure, we are glad to help you.
Thanks for pointing-out the errors in our original project:
1) No dimming, as was promised by the author.
2) Very dim LED.
3) Asymmetrical duty-cycle at the probes, contrary to the text.
4) No function with most original ICs at 3V or less.
Did your typing slip on the CD74HC132?
Sorry, I meant to type CD74HC132.
By the way, do you think that wit the suggested modifications the
circuit will show a linear response respect to the media conductivity?
I plan to measure the conductivity of salts dissolved in water from 0
parts per million to 3000 parts per million.
This is equivalent ( roughly) to a conductivity range of 0 mSiemens/cm to 4 mSiemens/cm.
Will your changes provide a linear response to increased conductivity?
( Twice salt concentration = twice conductivity = twice output from
the circuit ??? ) I plan to rectify the output signal to the LED.
By the way, do you think that wit the suggested modifications the
circuit will show a linear response respect to the media conductivity?
I plan to measure the conductivity of salts dissolved in water from 0
parts per million to 3000 parts per million.
This is equivalent ( roughly) to a conductivity range of 0 mSiemens/cm to 4 mSiemens/cm.
Will your changes provide a linear response to increased conductivity?
( Twice salt concentration = twice conductivity = twice output from
the circuit ??? ) I plan to rectify the output signal to the LED.
audioguru2
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JLB,
I tried my circuit with the probes in a glass of tap water, then activated-charcoal-filtered water. They both made the LED dim, like a 470 ohm to 2.2K resistor, depending on how much (1/8 inch to 1 inch) of the narrow (like a toothpick) probes was in the water. My probes are spaced 0.6 inches apart. Is my water that bad?
I have my trimpot set to maximum (100K) and it works well that way for soil resistance. When I reduce the trimpot, then the circuit becomes an on-off switch, because then the added capacitor seems to be too small.
Then I increased the capacitor to 11nF (11 times) and decreased the trimpot to 9K and the LED brightness responded to a resistance from 39 ohms to 5k (1/11 of before). The plain water dimmed like a 1.2K resistor. Then I mixed a level teaspoon of iodized table salt in 16oz of water (it didn't taste stong) and the LED became dim like an 82 ohm resistor. I don't know how many ppm that is but I think that I am on the right track. A limit will be reached where the CD74HC132 just cannot supply enough current to a very low resistance.
You do not need to rectify the pulse-width-modulated signal to the LED, just a series resistor and a filter capacitor to ground will be fine. Your DC voltage is measured across the filter capacitor. With a 3V supply, infinite resistance measures 1.5V, and a shorted resistance measures 3.0V. The voltage change certainly isn't linear with resistance change but appears to be logarithmic. It is difficult to tell since how much is 1/2 of infinity, and how much is double a short?
The symmetry of the waveform across the probes is not exactly 50-50 as I thought. It is actually about a 60-40 duty cycle since the oscillator's Schmitt threshold is less than 1/2 supply voltage.
I hope that you can still use this circuit.
I tried my circuit with the probes in a glass of tap water, then activated-charcoal-filtered water. They both made the LED dim, like a 470 ohm to 2.2K resistor, depending on how much (1/8 inch to 1 inch) of the narrow (like a toothpick) probes was in the water. My probes are spaced 0.6 inches apart. Is my water that bad?
I have my trimpot set to maximum (100K) and it works well that way for soil resistance. When I reduce the trimpot, then the circuit becomes an on-off switch, because then the added capacitor seems to be too small.
Then I increased the capacitor to 11nF (11 times) and decreased the trimpot to 9K and the LED brightness responded to a resistance from 39 ohms to 5k (1/11 of before). The plain water dimmed like a 1.2K resistor. Then I mixed a level teaspoon of iodized table salt in 16oz of water (it didn't taste stong) and the LED became dim like an 82 ohm resistor. I don't know how many ppm that is but I think that I am on the right track. A limit will be reached where the CD74HC132 just cannot supply enough current to a very low resistance.
You do not need to rectify the pulse-width-modulated signal to the LED, just a series resistor and a filter capacitor to ground will be fine. Your DC voltage is measured across the filter capacitor. With a 3V supply, infinite resistance measures 1.5V, and a shorted resistance measures 3.0V. The voltage change certainly isn't linear with resistance change but appears to be logarithmic. It is difficult to tell since how much is 1/2 of infinity, and how much is double a short?
The symmetry of the waveform across the probes is not exactly 50-50 as I thought. It is actually about a 60-40 duty cycle since the oscillator's Schmitt threshold is less than 1/2 supply voltage.
I hope that you can still use this circuit.
Audioguru, Thanks again.
If you mixed a level teaspoon of salt ( about 5 grams) in 19 oz ( 454 grams ) of water you had some 11,000 ppm solution.
Your probe is simmilar to the one I use, so your info is very interesting.
I will see if I can overcome the alinearity .......... or live with it.
Best regards, JLB.
If you mixed a level teaspoon of salt ( about 5 grams) in 19 oz ( 454 grams ) of water you had some 11,000 ppm solution.
Your probe is simmilar to the one I use, so your info is very interesting.
I will see if I can overcome the alinearity .......... or live with it.
Best regards, JLB.
audioguru2
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Hey Guys,
Last night, after watering my plants, I turned-off the lights and noticed that the LED on my slightly-modified project was very, very dim. I never looked at it in the dark before. I previously replaced the useless 100K trimpot with 220K so that the LED wouldn't indicate wet, low-resistance soil.
Replacing the soil with a resistor, the LED reliably indicates a smoothly changing brightness from 39 ohms to 100K ohms, a range of more than 2,500! ;D
I tried a PNP transistor with emitter resistor and voltage reference on its base as a current-source, to replace R4 which caused the LED to dim when the battery voltage ran-down to 2V. It didn't make much difference. So I tried Ante's trial-and-error method and ended-up with that PNP current-source directly driving the LED and the voltage reference being driven by the CD74HC132. It worked very well with a supply voltage from 2.3V up to 6V (the IC's limit). But since it also dimmed the LED below 2.3V, I gave-up and are now using the much simpler R4 instead, to current-limit the LED, and stay with a 3V battery. The dimming down to 2V isn't much. :-\
Last night, after watering my plants, I turned-off the lights and noticed that the LED on my slightly-modified project was very, very dim. I never looked at it in the dark before. I previously replaced the useless 100K trimpot with 220K so that the LED wouldn't indicate wet, low-resistance soil.
Replacing the soil with a resistor, the LED reliably indicates a smoothly changing brightness from 39 ohms to 100K ohms, a range of more than 2,500! ;D
I tried a PNP transistor with emitter resistor and voltage reference on its base as a current-source, to replace R4 which caused the LED to dim when the battery voltage ran-down to 2V. It didn't make much difference. So I tried Ante's trial-and-error method and ended-up with that PNP current-source directly driving the LED and the voltage reference being driven by the CD74HC132. It worked very well with a supply voltage from 2.3V up to 6V (the IC's limit). But since it also dimmed the LED below 2.3V, I gave-up and are now using the much simpler R4 instead, to current-limit the LED, and stay with a 3V battery. The dimming down to 2V isn't much. :-\
audioguru2
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Ante,
Yea, I actually had to try out different resistors (tweaking) and exercise my solder-sucker for a change.
It was because my LED current source didn't work as designed, since it was operating with only a 2V supply while powering the 1.8V LED, and didn't have much voltage remaining to control itself. The transistor wasn't saturated but refused to work properly when its collector voltage became less than its base voltage.
Yea, I actually had to try out different resistors (tweaking) and exercise my solder-sucker for a change.
It was because my LED current source didn't work as designed, since it was operating with only a 2V supply while powering the 1.8V LED, and didn't have much voltage remaining to control itself. The transistor wasn't saturated but refused to work properly when its collector voltage became less than its base voltage.
audioguru2
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To All,
What did I get myself into?:
"Hey, what's that thing? For the plants? Cool, can you make me some?"
Do you know how many times I have heard that in the past few days? This dumb project is becoming very popular with my friends. ;D ;D
A few minor bugs: :
1) When carrying the project with the probes bare, the LED is fairly bright. But occasionally, when the probes are inserted into very dry soil that happens to have a resistance that is close to the setting of the trimpot and its series resistor, the LED turns off. It stays off until the resistance of the soil changes a fair amount (or if you remove it and re-insert it).
This bug is caused when the resistances are equal, because that is when the signal at probe P2 is cancelled. When the probes are bare, the signal at P2 ramps to logic high and low levels. But if you suddenly cancel that signal at a moment when P2 is low, then P2 never gets high enough to trigger its gate's high Schmitt threshold voltage (1.5V max. with a 2V supply), so the gate stays off.
This bug rarely happens, maybe once in 20 tries. I can't easily fix it.
2) When the resistance of the soil equals the resistance of the trimpot and its series resistor, the LED is bright. But when the resistance is much higher or the probes are bare, the LED dims a bit.
This bug can probably be fixed by reducing the value of the capacitor at P2. Then the occurance of bug #1 above happening will be even rarer.
3) The LED really does dim a lot when the battery runs-down to 2V. The LED's current drops 77 percent because the IC gets tired with only a 2V supply. An added LED driver transistor will reduce the dimming to only 33 percent, which is barely noticable.
What did I get myself into?:
"Hey, what's that thing? For the plants? Cool, can you make me some?"
Do you know how many times I have heard that in the past few days? This dumb project is becoming very popular with my friends. ;D ;D
A few minor bugs: :
1) When carrying the project with the probes bare, the LED is fairly bright. But occasionally, when the probes are inserted into very dry soil that happens to have a resistance that is close to the setting of the trimpot and its series resistor, the LED turns off. It stays off until the resistance of the soil changes a fair amount (or if you remove it and re-insert it).
This bug is caused when the resistances are equal, because that is when the signal at probe P2 is cancelled. When the probes are bare, the signal at P2 ramps to logic high and low levels. But if you suddenly cancel that signal at a moment when P2 is low, then P2 never gets high enough to trigger its gate's high Schmitt threshold voltage (1.5V max. with a 2V supply), so the gate stays off.
This bug rarely happens, maybe once in 20 tries. I can't easily fix it.
2) When the resistance of the soil equals the resistance of the trimpot and its series resistor, the LED is bright. But when the resistance is much higher or the probes are bare, the LED dims a bit.
This bug can probably be fixed by reducing the value of the capacitor at P2. Then the occurance of bug #1 above happening will be even rarer.
3) The LED really does dim a lot when the battery runs-down to 2V. The LED's current drops 77 percent because the IC gets tired with only a 2V supply. An added LED driver transistor will reduce the dimming to only 33 percent, which is barely noticable.
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audioguru2
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Hi Guys,
After making a bunch of this project but modified my way, I have realised that it is as boring as watching grass grow. It also eats the two AAA alcaline batteries (AA are too big and heavy) in about 3 weeks.
So I have decided to spice it up a notch, save battery power and give a low battery indication:
1) Instead of the LED being on continuously, make it flash at 1Hz. It will still show the dimming effect, where wet soil is very dim then gets brighter and brighter as the soil dries.
2) Make the duty-cycle of the flashing low, so that the LED is lighted for only about 50ms-100ms each second. This will allow the batteries to last 10 to 20 times as long.
3) Make the duty-cycle change when the batteries are low. New batteries will make a 5/95 to 10/90 duty-cycle and low batteries about 60/40.
It is easy to do all these things by using a spare NAND gate as the flash oscillator, addind 2 transistors as a NOR gate and LED driver, adding a resistor and diode for the duty-cycle and allowing the voltage-drop across the diode to control the duty-cycle change at low battery voltage. It fits on a Veroboard the same size as the dual AAA cell holder. The revised circuit is here:
View attachment 35457
After making a bunch of this project but modified my way, I have realised that it is as boring as watching grass grow. It also eats the two AAA alcaline batteries (AA are too big and heavy) in about 3 weeks.
So I have decided to spice it up a notch, save battery power and give a low battery indication:
1) Instead of the LED being on continuously, make it flash at 1Hz. It will still show the dimming effect, where wet soil is very dim then gets brighter and brighter as the soil dries.
2) Make the duty-cycle of the flashing low, so that the LED is lighted for only about 50ms-100ms each second. This will allow the batteries to last 10 to 20 times as long.
3) Make the duty-cycle change when the batteries are low. New batteries will make a 5/95 to 10/90 duty-cycle and low batteries about 60/40.
It is easy to do all these things by using a spare NAND gate as the flash oscillator, addind 2 transistors as a NOR gate and LED driver, adding a resistor and diode for the duty-cycle and allowing the voltage-drop across the diode to control the duty-cycle change at low battery voltage. It fits on a Veroboard the same size as the dual AAA cell holder. The revised circuit is here:
View attachment 35457
audioguru2
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Hi guys,
My "flashing LED" revision that I made to this project works perfectly. ;D ;D
Since the LED is powered for such a short time, 2 AAA batteries will last a long time. The flashes are bright when the soil is dry, attracting your attention before the thirsty plant wilts. It even flashes through wilted leaves that might hang in front!
I added a resistor across the probes to reduce the modified project's soil-resistance range, and to fix the problem that happened without it, when sometimes the LED stayed off if the probes were suddenly given a soil resistance that equalled R2 (cancelling the signal at P2).
I'll post this flasher as a new project.
My "flashing LED" revision that I made to this project works perfectly. ;D ;D
Since the LED is powered for such a short time, 2 AAA batteries will last a long time. The flashes are bright when the soil is dry, attracting your attention before the thirsty plant wilts. It even flashes through wilted leaves that might hang in front!
I added a resistor across the probes to reduce the modified project's soil-resistance range, and to fix the problem that happened without it, when sometimes the LED stayed off if the probes were suddenly given a soil resistance that equalled R2 (cancelling the signal at P2).
I'll post this flasher as a new project.
audioguru2
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Ante,
As a soil moisture indicator, two 1000mA/hr (to 1.0V) alcaline AAA batteries should last a couple of years! The PWM of this circuit is logarithmic, so when the resistance of the soil is half-way to being very dry, the power to the LED is not also half, but actually only 1/10th, which looks like about half-brightness. Most of the time the resistance of the soil is much less than that, therefore the average current is very low. After all, this circuit is CMOS.
With new batteries and very dry soil, my circuit pumps 35mA through the LED, so it is very bright, but with a (flashing) low duty-cycle to extend battery life. The original circuit put only 1mA through the LED, which was very dim, and that was at its brightest.
As a soil moisture indicator, two 1000mA/hr (to 1.0V) alcaline AAA batteries should last a couple of years! The PWM of this circuit is logarithmic, so when the resistance of the soil is half-way to being very dry, the power to the LED is not also half, but actually only 1/10th, which looks like about half-brightness. Most of the time the resistance of the soil is much less than that, therefore the average current is very low. After all, this circuit is CMOS.
With new batteries and very dry soil, my circuit pumps 35mA through the LED, so it is very bright, but with a (flashing) low duty-cycle to extend battery life. The original circuit put only 1mA through the LED, which was very dim, and that was at its brightest.
audioguru2
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Kiew,
Sorry for the delay. I am finishing typing the modified circuit as a new project. It will be posted very soon.
I have made many circuits and they all work the same and very well.
Sorry for the delay. I am finishing typing the modified circuit as a new project. It will be posted very soon.
I have made many circuits and they all work the same and very well.
audioguru2
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Hi Kiew,
I have submitted my new project "Plants Watering Watcher-2". But since it is Saturday evening in Greece, I don't know how soon that Admin can post it. Look for it on the "Home" page. ;D ;D
I have submitted my new project "Plants Watering Watcher-2". But since it is Saturday evening in Greece, I don't know how soon that Admin can post it. Look for it on the "Home" page. ;D ;D
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