Automated Elephant feeder


A MOSFET, transistor or a relay.

What kind of animal eats elephants?

A MOSFET, transistor or a relay.

What kind of animal eats elephants?

I wanna see the size of the pins that hold the nine elephants up in the feeder. How far does it drop them?

On a serious note, for what you want to do, you would probably do better to provide a separate 24V source. You might even get your 5V for the Arduino off of that with a regulator. But that's another discussion. Power each through a logic level MOSFET (usually has an L in the name, ask here if you're not sure) off of that 24V power supply and use the Arduino to switch the MOSFETs. There are tutorials all around for driving a load with a MOSFET and an Arduino.

Have you considered just a relay?

Is the 24V AC or DC?

How much current is the 24V circuit?

To open the latch do you need to just pulse the latch or keep 24V ON all the time in one position?

Thanks.. Tom... :slight_smile:

What is the most efficient way to boost an Arduino's output to 24V?

OK, it seems you are a bit vague on the terminology here.

You use a 24V (presumably DC, but are you sure it is not AC?) power supply to power the latches, and you use logic-level FETs to switch that 24 V to the latches in turn.

In any case, if you were to use a switchmode converter to convert 5 V to 24 V, you would require five times the current (well, actually six or more times) at 5 V as the latches would use at 24 V. Now an Arduino can only supply 20 mA (twenty milliamps) from an output pin in any case, so you would still need a FET to switch that really heavy current (possibly several amps) from your 5 V power supply (which of course you also use to provide power to the Arduino itself via its 5 V pin).

So the problem is that you have not told us anything useful in order to help you. :astonished:

You need to give us a Web link to the latches, or else tell us their exact specification - operating voltage and operating current or resistance, confirm that they in fact operate on DC and not AC.

No-one here knows what "a PLC signal converter" is either, or else they would have no idea what one you were talking about. It is you see, the details that matter. :grinning: Without details, you are talking nonsense.

I would go with 9 relays.

Whatever it is you are driving would be able to be powered from the relay and the relay would be able to be powered from the Arduino. all very simple. pre-101 stuff

As a note, when you are asking how to control a thing, it would help greatly if you post a link to that thing.

As for costs. I cannot fathom how many bales of hay an elephant eats a day or how many peanuts, but the cost of almost anything in the Arduino world seem small.

Thanks for the info.

Your solenoid pulls 1.1A when activated.
The PLC signal level converter will not be able to do the job as it cannot conduct that amount of current, the converter is for low current signals.

You require a power MOSFET or Relay to do the job for each solenoid, not a converter.

Tom.... :slight_smile:

Pretty much any Arduino-compatible relay shield will control those locks. Your biggest problem will be getting 9 relays on one board.

I imagine that 8-relay boards are available but 9 will be rare. Maybe the 9th goes on a separate relay module connected to the Arduino with flying wires.

Power supply for the relays themselves will be an issue. Will you ever turn all 9 on at the same time? Then the power consumption will be too much to run from the Arduino 5V supply. But if it's only one or two then it should be OK to use 5V-powered relays.

Will you be deriving the Arduino power from the large 24V supply? It should be possible to find a car/truck phone charger that will give good 5V from 24V input.

And the arduino will be powered straight from a wall outlet

You need some sort of AC to DC converter there. If you plug it straight into the wall you're going to blow it up.

You need a relay with contacts rated for 24V or higher (32V is common) and 1.6A DC. Note the AC ratings may be higher because it is "easier" to switch AC. Over-rating is fine: 3A 240V would also work.

The coil voltage is important too, but not fixed, as I said above.

Something sold specifically for Arduino is advantageous but not necessary.

If you push 24VAC through a relay rated for 120VAC then you will only get 24VAC regardless of 120VAC rating. Rating is just maximum here.
Just as important is the max current rating, cheap relays I've seen can carry 5A to 10A.

Fun thing, AC and DC switches are made different since DC switches opening drag sparks that AC would interrupt, DC switches need a larger gap. Yes, I was surprised to learn that.

OK, a few things now.

Firstly, you need a 24 V DC power supply. What do you propose to use? Note it does not need to be regulated, but switchmode power supplies - which are all regulated by definition - are readily available and cheap. It has to be generously rated for however many solenoids you wish to simultaneously actuate. Three at a time? 1.6 A each? Total 4.8 A, look for a supply rated from 6 to 10 A. 10 A would be good in case you want to actuate 4 or 5 at a time in the future.

Next, you only want to operate the solenoids for one second, and not repeatedly, do you not? That is important in various ways. It means the switching device doe not need to be rated for continuous use as I next explain. It means the power supply might not need to be rated for continuous use but actually, it will be. Most significantly, those solenoids - not mentioned on the listing - are in any case not rated for continuous actuation - a few seconds only - as in your or in fact, virtually any application. If they were on a door with a digital lock (most usual application) they would only actuate for 10 seconds at the very most to allow the door to open.

Al that taken into account, I suggest you use the readily available IRF520 modules rather than relays.

There is much said about the IRF520 not being a logic-level FET but actual reference to the datasheet figure 2 indicates that (worst case) at 2 Amps with 4.5 V on the gate, it will have less than 300 mV across it and thus dissipate less than 600 mW which it may well be able to dissipate continuously with no heatsink, but for a few seconds only will clearly be very safe.

This avoids the need for a relay supply. Presumably you will use an Arduino Nano; you will want a 24 V to 5 V switchmode converter to power the Arduino and with these modules, you could use a "Nano expansion board" and three pin "servo" cables to easily assemble the whole control system, with heavier wiring to the screw terminals of the FET modules and power supply.

Note finally that whatever you use to control them, you must have 1N5401 diodes connected in reverse across each latch solenoid. These can be fitted across the "V+" and "V-" terminals of the above modules. All wiring to the power supply and solenoids must be paired using "figure 8" or domestic lighting fixed wiring cable.

The relay can't destroy anything.

IRLZ44N doesn't come on a module I know of .... and a quick search turns none up but they're cheaper than relays, I bought 60 for just under $10, 14.5 cents each.

But that does not include a heatsink (piece of metal) or gate resistor or terminals and board however the full open gate takes 2V.

300mA is 100mA more than the max total current that Uno pins can sink and/or source without damage.

If this is all going to be in an enclosure - and it should be - I’d be inclined to something like this:
24 Volt Open Frame Power Supplies | 24Vdc Open Frame Power Supplies in Stock | 5 - 500 Watts | TRC Electronics.

Additionally, since there are electrical safety i$$ue$ here, and you admit your inexperience, you may want to consider having a qualified electrician build this for you.


Or is there a better option? Keep in mind that I have very limited experience wiring anything.

#16? :roll_eyes:

An electrician may be used to contactors which work at 24 V AC. For a DC relay, you want a switchmode power supply which gives regulated DC.

This may not be the place to get this information, but google searches aren't getting me where I need to be.

Well, for better or worse, this is very much the place to get this sort of information. :grinning:

So I bought a relay (

Web link corrected. OK, so you ignored my advice in #16. Oh well! :roll_eyes:

Note this relay module runs on 5 V.

That I'm planning on powering with this (EPP-150-24 - MEAN WELL - TRC Electronics).

Not a bad choice. Its continuous current rating without a fan is 4.2 A, however for your intermittent (and very short term) operation, you can consider it 6.25 A. Possibly slightly more. So you may want to actuate as many as three of your 1.6 A latches at any one time, totalling 4.8 A. Since it will be only brief, that is perfectly safe.

According to the specs for the power supply I need to get some JST VHR connectors. It says that the output has two neutral wires and two hot wires and I'm not sure how that connects to the relay.

The 24 V power supply has nothing whatsoever to do with the relays; it power only the latches. Note the need to have a "flyback" diode across the connections to each of the latches.

Those connectors are commonly referred to as "Molex" connectors and were used for the power supply connections of the original IBM PC motherboards. If you can find a really old PC power supply, you could use the leads, cut down to suit. Note the importance of connecting a mains ground to the frame of that power supply. :grinning:

It may be convenient to use a 24 to 5 V switchmode "buck" converter to derive 5 V for the relay module. The 5 V supply connects to "JD-VCC" and "GND" on the right hand side of that relay module with the jumper removed. You must ensure the power and ground wires all travel together as a pair. You should put a 470 µF or so capacitor directly across the 5 V power connections at the relay module. You should probably solder these connections rather than use "Dupont" wires,

The Arduino - presumably a Nano as UNOs are not very practical for "real world" designs - connects to the "VCC" and the adjacent "IN" pins of the relay board. It does not connect to the "GND". Dupont wires are probably adequate.

You may be able to power the Arduino from the same 5 V supply as the relays but the connections to 5 V and ground must travel again as a pair back to the 5 V supply itself, separately to the relay supply connections.