hi & need help

[ronp849]

Hi - One thing you need to watch is earthing. The probe signal currents are very low so an earthing leakage path could distort the readings.

Ie - Probes -> Soil -> Earthed power supply -> Power supply ground -> probes

Also are the Individual Plant Pots electrically isolated? - Electrical leakage between them could also distort the readings.

 

[ericgibbs]

hi eric

would you look at this list at tell me if it looks ok for what i need ?


hi Scott,

[B]Parts for the basic sensor kit.[/B]
Power suppply:
Qyt:
1	240/6Vac  3VA min
1	Fuse and Holder 200mA
1	1N4001 diode
1	7805 reg
1	470uF 16V cap
1	10uF 16V cap
1	Plastic enclosure

Indicator Unit:  [for 1 plant]
1	LM3914
10 	LED's
1	1N4148 diode
1	100K 0.25W resistor
1	2K2   0.25W resistor
1	2K7   0.25W resistor
1	100nF cap
1	10uF 16V cap
1	500K linear pot, low cost
1	pcb

Ref the pot in your posted list, its far too expensive for this project.!

The type I would use are a 500K of:
VISHAY SPECTROL|64W-502|TRIMMER, 24 TURN 5K | CPC

If you decide to build the last circuit using the 4066 ic. let me know and I'll update the parts list.

 

[ronp849]

Looking at the original cct, there will be a current inbalance between the positive and negative half cycles. The negative cycle will produce a current through the 500k pot only while the positive half cycle will be through the pot and the 100k resistor in parallel. The diode will make the waveform even more complicated with its forward voltage drop. This will give a positive DC current which the use of the transformer was trying to eliminate.

I have used a similar set of probes for water level detection. I did not use AC but a very narrow energising pulse to take a reading every 30-seconds or so. The energy was so small there was no sign of electrolytic action on the probes.

This method did use a processor however.

Ron

 

[haggis@home]

hi Scott,
Which circuit are you going to build.????

hi Eric ..

i was going to knock up the last one you posted , as you wanted me to do the bench test with a dmm . one other thing i was studying the schematic last night for the original circuit , looking at the pick up for the probe is it not dc ? as the pickup is after the transformer on the 6V side ? .

i can ditch the pc psu if it makes things easier ? , and thanks for the tip on the pot . i did think it was a bit Pricey , i did not think that one like that would work . so that will save me a fair bit of cash .... thank you

 

[Mike_2545]

I don't even want to know what you would have to do to "knock up" a circuit...

eewh...

 

[haggis@home]

I don't even want to know what you would have to do to "knock up" a circuit...

eewh...

mmmmm circuit ... well i think you would have to get it turned on first and then get your logic probe out

 

[Mike_2545]

I could have gone the rest of the day with out that image in my head...

 

[ericgibbs]

hi Eric ..

i was going to knock up the last one you posted , as you wanted me to do the bench test with a dmm . one other thing i was studying the schematic last night for the original circuit , looking at the pick up for the probe is it not dc ? as the pickup is after the transformer on the 6V side ? .

i can ditch the pc psu if it makes things easier ? , and thanks for the tip on the pot . i did think it was a bit Pricey , i did not think that one like that would work . so that will save me a fair bit of cash .... thank you

hi Scott,

I don't even want to know what you would have to do to "knock up" a circuit...

hi Mike, Knock up is like 'cobble up'.....

This is the full parts list.

Parts for the modified sensor kit. Circuit dated: 04/03/2009

Power suppply:
Qyt:
1	240/6Vac  3VA min
1	Fsue and Holder 200mA
1	1N4001 diode
1	7805 reg
1	470uF 16V cap
1	10uF 16V cap
1	Plastic enclosure

Indicator Unit:  [for 4 plant]
1	LM3914
10 	LED's
4	1N4148 diode
4	100K 0.25W resistor
1	2K2   0.25W resistor
1	2K7   0.25W resistor
1	100nF cap
4	10uF 16V cap
4	500K linear pot, low cost
1	pcb 

CMOS: etc
1	HEF4017
1	HEF4066
1	HEF4093
4	LED's
4	LED resistors
1	47uF 16V cap
2	100nF cap
3	100K resistor
1	470K resistor
1 	no/ push switch
1	SPST switch
1	100uF 16V cap

 

[Mike_2545]

On this side of the pond:
"Mock up" is [noun a model, often full-size, for study, testing, or teaching: a mock-up of an experimental aircraft.]

"Knock up" is [impregnate,inseminate, procreate]

Big difference, but funny in this case...

 

[ericgibbs]

On this side of the pond:
"Mock up" is [noun a model, often full-size, for study, testing, or teaching: a mock-up of an experimental aircraft.]

"Knock up" is [impregnate,inseminate, procreate]

Big difference, but funny in this case...

How about a 'lash up', thats like a 'knock up' but more fun.

 

[Mike_2545]

"Lash up" can lead to "knocked up" if you don't "mock up" the proper protection.

 

[haggis@home]

thank you Eric .. i will get costing it up , would you know any one who could make the pcb for me (willing to pay good cash)

so it looks like i priced up the wrong transformer then ? also on the list you have put led resistors , any idea what ohmage they would be ?

 

[haggis@home]

"Lash up" can lead to "knocked up" if you don't "mock up" the proper protection.

muhaahahahahah ... good point

 

[ericgibbs]

thank you Eric .. i will get costing it up , would you know any one who could make the pcb for me (willing to pay good cash)

so it looks like i priced up the wrong transformer then ? also on the list you have put led resistors , any idea what ohmage they would be ?

hi,
Ref the leds, do you want different colours for some of the 10 levels.

Say Red for 1,2,3,4 Yellow for 5,6,7 Green for 8,9,10

I would build a small circuit of this type on vero board/stripboard.

The 4 leds on the 4017 could be any colour you choose.

I would like to see what voltages you get for dry,damp, moist, watered pots.....