| Electronics > Beginners |
| gear 0.2 |
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| uc:
Dear CatalinaWOW, I am not planning to buy readymade one. I am not planning to do “reverse engineering” of existing one. This is just a interesting project for me, creating things in a safe manner. Q1 you say “They all use 24 AC” Could you please explain this? I do not understand. |
| rstofer:
It simply means that common sprinkler valves use 24 VAC for the coil. They may, or may not, work on DC. Let's assume they don't... Since it is 24 VAC, you can't control them with a single transistor or MOSFET but you can control them with a TRIAC. Even better is an optically isolated TRIAC because it separates the logic voltages from the coil voltages. Here is a project that comes from right here at EEVblog: https://www.eevblog.com/forum/beginners/circuit-to-control-sprinkler-system-with-arduino/ Regardless of the uC versus <whatever> control scheme, you need some way to actuate the valves. The TRIAC circuit in this document is pretty nice. I would want to test some valves to make certain they didn't require more than 1.0 Amps. Simple test, rig up a 24VAC transformer and run the current through a DMM in series with the valve. It's important! If the current is more than 1.0A then you have to a) come up with a TRIAC than can handle more current or b) use a relay. The relay might as well be 24VAC (common supply voltage) and it can be controlled by a TRIAC. There's no way a small relay requires anything like 1.0A. I would probably use the relay in either situation because a short circuit in the solenoid valve might wipe out the relay but it probably wouldn't damage the rest of the system. BTW, fuse the 24VAC to protect the relay and wiring. https://www.digikey.com/products/en?keywords=VO2223 This is where the numbers start hitting the project. There's a lot to think about when picking parts. |
| CatalinaWOW:
All of the commercial ones that I am aware of operate the solenoids on 24 V AC. There are a few reasons for this. One, these systems operate in a wet environment in the presence of untrained people like your wife. Use of a relatively low voltage makes this safer. Two, this low AC voltage is easily derived from the mains using a transformer. This transformer also isolates the low voltage supply - another safety feature. Three, 24 volts as opposed to some other low voltage because this voltage had already been standardized for use in doorbell and HVAC applications, reducing the cost of components. Good luck with your project. I would suggest using the standard irrigation valves. Not much electronics to learn there, and lots of hydraulic and mechanical problems worked out and approved for connection to public water systems. |
| bingo600:
I find a lot of 12v solenoids if i do this search on ebay.com: water valve solenoid @uc make sure to make a "low point" water tap. For emptying the valves & tubes , when (before) it gets freezing ... I had to replace the water solenoid on my washing machine, back in 2008 when it was -28C outside and unfortunately freezing i "Torpen" Was lucky it didnt break the pipes /Bingo Edit: For this price (and free shipping to Sweden for orders over 39€) , i'd consider buying. https://www.amazon.de/GARDENA-Bew%C3%A4sserungscomputer-EasyControl-Bew%C3%A4sserungssteuerung-Batteriebetrieb/dp/B00GHEH8OE/ref=sr_1_1?ie=UTF8&qid=1527413709&sr=8-1&keywords=wasser+automatik Misc fittings you'd need anyway https://www.amazon.de/dp/B074CFLFW9/ref=sspa_dk_detail_5?psc=1&pd_rd_i=B074CFLFW9&pf_rd_m=A3JWKAKR8XB7XF&pf_rd_p=2444543729105426210&pf_rd_r=0HGWY7SAAM28C68W97EF&pd_rd_wg=AwsyO&pf_rd_s=desktop-dp-sims&pf_rd_t=40701&pd_rd_w=i8Pt0&pf_rd_i=desktop-dp-sims&pd_rd_r=cb4a5b4e-6191-11e8-b22f-9be43c3b90dc |
| larsdenmark:
If you aim for the timer based solution then you can get a timer IC: http://www.ti.com/product/LM555 There are many companies that produce such ICs and they all end with the number 555. This IC can be used for a lot of things are quite cheap so you may wish to grab 10-20 of these for various experiments. This IC is an analog IC so there is no programming involved. You use resistors and capacitors to control the timing so you should get a collection of these as well. Unfortunately the 555 is not able to tell the time precisely, but I don't think the plants will mind that the timing shifts a little. Also the 555 is not stable for long intervals so I suggest that you create a system that starts the water flow every hour and let the water run for a short time. You can use another 555 to control how long time the water should flow for. You most likely want a potentiometer to be able to vary the duration. You need a solenoid valve to control the flow. I would recommend something that runs on 12 V. This will mean that you can run the entire circuit on the same voltage as the 555 has a maximum of 18 V (at least the one I link to). You want a valve that is turned off when the power is off (so you don't flood anything if the power goes away). You need a diode across the solenoid in order to protect the circuit. You can't control the solenoid directly from the 555 unless you can find a solenoid that uses very low current. Hence, you need something to drive the solenoid from the output of the 555. I would recommend a relay since these are simple to set up (you also need a diode across the relay in order to protect the rest of the circuit). For slightly more advanced solutions you can use a transistor (BJT) or a MOSFET (which is also a kind of transistor). This should amount to a nice DIY project and fiddling with the 555s means that you'll be able to use the scope to monitor all its signals! |
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