DIY misting sensor for cuttings

[shibui]

In a recent thread on growing cuttings I mentioned having made my own mist controller for the cutting bed.
This is a commercial unit

sage balance arm.PNG

$209.30 from Sage Horticultural but you need more than just the sensor.
These work when they are placed amongst the cuttings. When the mist comes on droplets gather on the mesh and make that end heavier until it tilts down which switches off the solenoid valve and stops the sprays. The mesh dries at the same rate as the cuttings and gets lighter. When it tilts back up it turns the valve on again and the mist starts until the sensor tips down again. In this way the cuttings are misted automatically whenever the leaves start to get dry but they do not get drowned with constant misting.
So as well as the balance arm you also need a solenoid valve. Because it works in or near water its not safe to use 240v electricity so you also need a transformer to supply 24v power to run the unit. (The transformer can also operate low voltage bottom heating if required). The full starter package is $430.00. If you are going to grow lots of cuttings its probably worth paying for a properly designed unit but if, like me, you like to make your own stuff and have more time than money here's how to make one yourself.

The balance arm sensor unit:

balance arm.png

The long rod is a light steel rod with one end threaded. The shorter rod is soldered or glued to provide the pivot point. The larger rectangle is the collector to gather drops of mist. I cut mine from fine stainless steel mesh (termimesh used to stop termites in buildings - try scrap metal dealers or builders for offcuts) Mine is about 20cm x 9cm which is larger than the commercial unit. I figured the larger size would be more sensitive to allow for other inaccuracies in my construction?? My neighbour started out with a thin kitchen sponge as his sensor pad but has upgraded to aluminum flywire. Bonsai pot mesh might even work ok. The sensor pad is glued to the long end of the balance arm - silicone sealer or construction adhesive works for this.
A counterbalance at the threaded end allows you to adjust the sensitivity. Mine has a few nuts and washers to provide the balance. You could also try fishing sinkers or lead weights.

The all important switch:
I've used a mercury switch from Jaycar. These are a lealed glass tube with wires through one end and a blob of mercury inside. When it tilts up the mercury runs to one end and touches the end of the wires inside the tube and completes the circuit. When it tips down the mercury runs to the other end and the circuit is switched off. You will have to ask for these at the counter and might have to convince staff you are not a terrorist before they will sell them to you. Prices - sm1035 - bare wires $2.75, sm1044 -in a plastic housing with 30 cm flexible leads $4.45
Tape, tie or glue the switch under the cross bar of the sensor arm.

Something to stand it on:
I bent up a housing like the commercial unit from light stainless sheet and drilled holes to take stainless bolts which I had drilled smaller holes in to hold the cross arm of the balance. This was the most difficult and inaccurate bit and I think I'd try just drilling smaller mounting holes in the housing and sitting the cross arm directly in these next time. My neighbours mount is much simpler - just a rectangular box from gal sheet with holes in the side for the cross arm to pivot in.

Mount the balance arm in the stand and make sure the lead from the switch does not impede the free movement. Adjust the counterweight until the mesh swings up. (If the mesh is too heavy trim a bit off until you can balance it properly). Lightly spraying the mesh should make it tilt down. Check that it slowly tilts back up as the moisture dries off the mesh collector.

PICT0002.JPG

All the other bits:
Now you need mist sprays over the cutting bed. I got proper ones from Sage hort. $15.40 each. They spray about 1m diam but you need to overlap the spray pattern to get full coverage so you'll need 2 or 3 for even a small cutting bed. The little red mist microsprays available at most nurseries and hardware stores might give an adequate mist cover at just a few $ each.
A solenoid valve turns the water on and off. You'll only need a small one 12 or 19 mm. Look at the hardware or irrigation shop. somewhere between $10 and $30 depending on brand and size.

Power supply: You need a low voltage supply for safety. Transformers designed to run garden lights should be adequate to operate a solenoid valve. Plug the power supply into a power point well away from the water and run the low voltage wires into the propagation area. I made my unit when there was no mains voltage available here so it runs on a car battery and a small solar panel to keep it charged. The solenoids are designed to run on 24v AC but operate just as well on 12v DC.

Connect it up:
One wire from the power supply connects to one of the mercury switch leads. The other power supply wire is connected to any one of the solenoid wires. The other solenoid wire is connected to the remaining mercury switch lead.
When the power is on and the sensor arm is tilted up power should run and open the solenoid switch letting water through the mist jets. As the collector mesh gets wet the arm should tilt down until the mercury switch opens and the water will stop.
I found that the 12v Dc was too strong for the mercury switch and they gradually stop working so I added a relay switch to the circuit so only a tiny current passes through the switch and the relay handles the full current to the solenoid valve.

You can adjust the sensitivity of the unit by moving the counter weight in or out along the long rod - further out means the cuttings will get more spray more often, move the weights further in for less spray. The threaded rod and nuts on mine are now rusted tight so I adjust mine by adding small horse shoes of copper wire to increase the weight and the watering and remove one or more to lighten it.

Now that is all as clear as mud. Anyone want to try????

[PaulC]

Hi Shibui,

thanks for taking the time to share this with us.

I for one am interested in setting something like that up at a later date,
so this will come in handy when the time draws nearer.

Thanks again.


Paul C.

[alpineart]

Hi Shibui , i'd better not let you in my shed , its filled with a complete unit that was removed from a custom built Orchid hothouse i picked up a few years ago .I have the mist sensor as per pic , heater , heated grow bed unit , misting units , waterproof lighting and the complete custom made arched hot house . The only thing missing was the soleniod switch for the auto sensor to switch the misting spays on . One day i might put it together or flog it off . Beginning to loose interest in my plants .Need a change of attitude for sure .

Cheers Alpine

[Damian Bee]

Make that 2 sheds to keep him out of

[bodhidharma]

Excellent post Shibui. Thanks for the effort.

[Bretts]

Great info Shibui

[Oldhilly51]

Just wondering if there have been any "improvements" made to the design of this sensor over the last couple of years? Mrs. Oldhilly is the Bonsai person, I just get to solve the construction and equipment problems as they arise.

[shibui]

That same sensor is still operating my misting system. The mesh needs cleaning a couple of times each year because algae grows on it in the constant moisture - just spray with vinegar and scrub it with a toothbrush.

[Oldhilly51]

Thank you, Shibui. I was wondering about the mercury tilt switch. They usually don't have much in the way of current ratings but I guess a single solenoid valve doesn't draw all that much current. I bought some stainless steel bolts at Bunnings yesterday and drilled holes in them to suit the brass rod I already have for the pivots, just need to work on the arm and "leaf material". I was thinking of using some stainless mesh from a camping toaster for the "leaf" and perhaps some old UHF TV antenna element for the arm, either way, it's going to cost a lot less than buying one.
Thanks for the idea.

[Jow]

Neil this is just the sort of project to have a go at...... After I get all the others finished.

[shibui]

They usually don't have much in the way of current ratings but I guess a single solenoid valve doesn't draw all that much current.

You are correct. While I had the mercury switch wired directly in the circuit passing all the current at 12volts DC they would only last a few months then stop working. You will note above that I added a relay - (Tandy or Automotive supplies) so that the mercury switch only handles enough current to trip the relay which is rated to handle 12v DC and high currents.

I was thinking of using some stainless mesh from a camping toaster for the "leaf" and perhaps some old UHF TV antenna element for the arm

Sounds like you are well versed in adapting and reusing. The only issue is joining different materials. I used silicon sealer to attach the stainless mesh to the rod but I don't think it would be a strong enough joint where the arm attaches to the pivot.
It also needs adjustable counterweight on the back so you can adjust the balance. My steel arm has a nut and a couple of large washers to provide adjustable counterweight but under constant moisture the nut has rusted onto the thread so no longer adjustable and now I make changes by adding or subtracting little horseshoe shaped bits of copper wire which occur in abundance around bonsai.
A brass rod would be easy to solder or braze to the pivot and would not rust. Stainless rod would also suit but I have no experience threading or joining stainless.

Good luck with the project. Happy to correspond if there's any further help I can offer.

[Oldhilly51]

Well, things are progressing slowly. A trip to Bunnings got me a couple of 10mm stainless bolts and nuts. I found some 10mm aluminum "U" channel for the swing arm and my scrap box contained some 5mm brass rod. The boys at Jacar didn't bat an eyelid when I asked for mercury tilt switches and 24V relays. I strongly suspect they are used to me asking for strange things by now. A trip to "Anaconda" got me a stainless toaster mesh, then it was back to Bunnings for a solenoid valve, some 1/2" poly tube and some rubber feet.
All-up the whole thing will cost me less than $35.00 but I had access to a lathe to bore out the stainless bolts plus I had quite a few of the other parts "on hand". The next real expense is going to be for the cover for the table all this is going to happen on. I have a wooden pallet (that I will cover with some sort of heavy plastic/vinyl to make it easy to clean) that is 800mm square. I mounted this on a set of legs so it's at a comfortable working height and thought that a clear plastic box about 450mm high by 800x800mm should just about be good enough for a trial run. I have a few plastic misting nozzles that are rated at 1M diam and will try with just one in the centre to start off with.
Comments and advice are more than welcome at this stage of events!

[shibui]

Sounds good so far.
Normally misting beds are made with a gravel bed base that the pots sit on. Heating wires are normally buried in the gravel but I have not added bottom heat to my beds. I have used old clip lock roof decking as the trays. Cut to the required length then fold up the ends so you have shallow trays that will hold water. Fill with 10mm gravel for the pots to sit on. When in use the trays hold extra water to provide bottom moisture and more humidity.
Try the vinyl cover first and see how it goes. Maybe gravel beds are not necessary without the bottom heat wiring?
Try with just one misting spray first but I suspect you will need a couple for even coverage. Most micro-sprays have a pattern that leaves a dry patch near the centre so the spray pattern needs to overlap to get even coverage.

[fossil finder]

Well, things are progressing slowly. A trip to Bunnings got me a couple of 10mm stainless bolts and nuts. I found some 10mm aluminum "U" channel for the swing arm and my scrap box contained some 5mm brass rod. The boys at Jacar didn't bat an eyelid when I asked for mercury tilt switches and 24V relays. I strongly suspect they are used to me asking for strange things by now. A trip to "Anaconda" got me a stainless toaster mesh, then it was back to Bunnings for a solenoid valve, some 1/2" poly tube and some rubber feet.
All-up the whole thing will cost me less than $35.00 but I had access to a lathe to bore out the stainless bolts plus I had quite a few of the other parts "on hand". The next real expense is going to be for the cover for the table all this is going to happen on. I have a wooden pallet (that I will cover with some sort of heavy plastic/vinyl to make it easy to clean) that is 800mm square. I mounted this on a set of legs so it's at a comfortable working height and thought that a clear plastic box about 450mm high by 800x800mm should just about be good enough for a trial run. I have a few plastic misting nozzles that are rated at 1M diam and will try with just one in the centre to start off with.
Comments and advice are more than welcome at this stage of events!

Love some pics if possible Oldhilly51. What a great idea!

Sent from my SM-T530 using Tapatalk

[shibui]

Here are a couple of photos of my cutting bed that might show a few more details.

P1140188.JPG

showing the copper wire loops that are used to adjust balance now that the counterweight is no longer adjustable.

P1140189.JPG

Please excuse the liverwort and general unruly state. I just sprayed the liverwort and moss with vinegar this week. Now brown, should be gone in a week or 2.

P1140190.JPG

Showing gravel trays, misting sprays and pots of cuttings. The chooks sleep in the cage under the propagating bed (entry from the chook run behind the igloo) Body heat and CO2 helps cuttings grow during our cooler months.

P1140191.JPG

There are lots of possible trays that will hold water and gravel but I had this stuff on hand. Use these full of gravel for propagating and on the shelves outside as humidity trays for smaller bonsai or, as in this case, for bog plants.

Love to see other ideas and setups for propagating, etc.