Introduction: Automatic Pet Feeder Using an Old Digital Watch

About: Everything Aquatic ---

Hi there, in this instructable I will be showing you how I made an Automatic Pet Feeder using an old Digital Watch. Ive also embedded a video on how I made this feeder. This instructable will be entered into the PCB contest and as a favor I would appreciate it if you voted for this instructable down below. It would help us to create more awesome projects and share it with you on instructables :D

There are many methods to create a pet feeder using micro-controllers, but there are many people out there who find micro-controllers to be a hassle. So I decided to make a pet feeder using a basic timer (a digital watch with an alarm function), so that the people who do not prefer micro-controllers are not left out of the electronics hobby.

The necessary Eagle files will be attached below.

HOW this circuit works, will be described at the end of the instructable.

The tools you will need for this project are:

  1. Helping Hand for Soldering (Optional)
  2. Flux
  3. Solder
  4. Soldering Iron
  5. Screw driver
  6. Bent Nose Pliers
  7. Wire Stripper
  8. Hot Glue Gun

Additional tools you will require if you choose to make your PCB at home:

  1. Rough Sponge
  2. Laser Printer
  3. Iron or Laminator
  4. Containers
  5. Ferric Chloride
  6. PCB Drill Bit
  7. Drill or rotary tool

The components you will need are:

  1. Single Sided Copper Clad Laminated Board (for DIY PCB)
  2. Magazine paper (for DIY PCB)
  3. Thyristor 2p4m - 2
  4. LM7805 Voltage Regulator - 1
  5. LM317 Adjustable Regulator - 1
  6. PC817 Opto-coupler - 2
  7. Resistor 1k - 1
  8. Resistor 820ohms - 2
  9. Capacitor 47uf 50v - 1 (can be increased if needed)
  10. Female Headers
  11. Male Headers
  12. Servo (Tower Pro-Micro Servo SG90) - 1
  13. Digital Watch with Alarm function (which does not beep every hour) - 1
  14. Mini push button switch (tall) - 3
  15. Copper Dot Board - 1
  16. Thin Flexible Wires
  17. 10k Potentiometer - 1
  18. 9 Volt Battery Connector - 1
  19. Miniature Slide Switch - 1
  20. Potentiometer Knob - 1
  21. Micro Switch
  22. Nuts and Bolts
  23. Small Plastic Container (to store the food)
  24. 9V Battery

Step 1: Designing the PCB (using the Eagle Software)

There are many softwares out there to choose from when you need to design a PCB. But the Autodesk Eagle software stood out to me since it is very professional and offers a huge component library which can still be expanded if you require, and provides a greater ability to customize the PCBs.

If you have never used Eagle before to make PCBs, download it for free right now.

I will attach the necessary Eagle files along with the pdf to print out the PCB.

Remember to print it out onto magazine paper using a laser printer. It did not work that well when I used glossy paper.

The setting should be set to "Actual Size" when printing, so that printout does not shrink or expand in size.

Step 2: DIY PCB at Home

I decided to go ahead etching my own PCB at home for a few reasons. Even though some companies offer to produce PCBs for a few bucks, their delivery charges are many times the price they charge for the PCB. In the end I found it to be an unnecessary expense and buying an actual Pet Feeder would have been more cheaper. I also like the satisfaction after I make my own PCB. Sure it is a bit tricky, but once you get the hang of it, the possibilities are endless.

The steps I took to prepare the copper board for etching are:

  1. I used a rough sponge to scrub off any dirt or oils (of the copper laminated board) so that the toner will stick well to the copper.
  2. After I dried the copper board, I placed it on the magazine paper, facing the printed side, and I taped it to a piece of paper.
  3. Afterwards I folded the paper in half, and began to Iron on it (the Iron should be increased to the maximum heat and the Steam turned off)
  4. I placed the iron on the side of the magazine paper, and ironed it for approximated 5 minutes.
  5. Afterwards I gently removed the copper board from the folded paper, and place it in water (be careful, it will be very hot).
  6. After letting the magazine paper soak up the water, I began to gently peel off the magazine paper from the copper board (take your time, when peeling it off).
  7. Thereafter I wiped it dry.
  8. I used a permanent marker to fill any gaps in the traces that may have formed when peeling off the magazine paper.

The steps I took to Etch the Copper Board:

  1. I used Ferric Chloride to etch the copper board. Please use caution when handling with Ferric Chloride.
  2. The copper starts to dissolve off little by little. The etching process may take approximately 10 minutes.
  3. When its complete, I rinsed it off in water and wiped it dry. (Do NOT leave it in the Ferric Chloride even after the unwanted copper is dissolved off, or else the traces will be eaten away as well).

Finalizing the PCB:

  1. I used a drill to punch in the necessary holes in the PCB.
  2. After drilling all the holes, I used steel wool to scrub off the toner, revealing the copper traces underneath.
  3. I used the steel wool on the other side as well, since the drilling process may leave it rough.
  4. I wiped it off, and it revealed a really nice printed circuit board.

Step 3: Soldering the Components Onto the PCB

Most people find soldering to be a tedious task. But if you follow the correct procedure, you will fall in love with soldering, and get the best solder joint possible.

  1. Make sure to always have an exhaust fan near your work bench to suck out the fumes from the flux burning (its actually the flux which causes the fumes, not the solder, and this is harmful to your lungs).
  2. Do NOT use gloves (this might sound counter-intuitive, but you are working with a tool which emits alot of heat, if it touches your gloves, you might not feel the burn until the gloves melt onto your hands. Trust me, you do not want burning rubber or latex on your hands.
  3. Always clean your tip before you solder every component. An oxidized tip will not create a perfect solder joint. Use a wet sponge (the ones made specifically for soldering, which do not melt, and they are pretty cheap). Do NOT use rough sandpaper to clean your soldering tip, the protective coating will wear off and you will be left with bare metal.
  4. Use flux (trust me, this helps a lot)

The components you will need to solder onto this PCB are:

  1. Thyristor 2p4m - 2
  2. LM7805 Voltage Regulator - 1
  3. LM317 Adjustable Regulator - 1
  4. PC817 Opto-coupler - 2
  5. Resistor 1k - 1
  6. Resistor 820ohms - 2
  7. Capacitor 47uf 50v - 1 (can be increased if needed)
  8. Female Headers
  9. Male Headers

Step 4: Modifying the Servo

Servo's cannot usually turn continuously. They are usually used with a micro-controller to adjust the position.

The steps I took to make it turn continously are:

  1. I took out the cover of the Servo after removing its screws
  2. I desoldered the wires from the circuit inside the servo, and connect it directly to the motor.
  3. I took apart the front cover which houses the gears, in order to remove the end stop which prohibits the servo from rotating continuously.
  4. But for some reason my servo did not have an end stop, so I put everything back in place.

The reason I used a Servo instead of a normal motor is because the servo can be easily mounted onto a casing, and also the fact that the food container can be fixed to it using just one screw.

Hits two birds with one stone.

Step 5: Modifying the Watch

Most wristwatches have an alarm function which uses a Piezo buzzer to notify you when a set time is reached. For this project you will need just that, but it should not beep every hour. Some watches have the hourly alarm, which would end up triggering the Feeder every hour. We do not want obese pets.

Here are the steps I took:

  1. I first tested out the alarm function and thereafter checked which button turns off the alarm. Seems like the button for the light turns off the alarm in this specific watch.
  2. Afterwards, I moved onto disassembling the watch.
  3. The two contacts which touch the piezo buzzer is what sends it the signal, and we will need these terminals to trigger our circuit.
  4. The buttons work by touching the common contact to the terminals on the circuit of the watch.
  5. After unscrewing the battery holder plate, I broke off the common contacts which acts as the buttons.
  6. I soldered in a wire to the plate so that I can use it as a common contact.
  7. I soldered in another wire to the terminal which connects to the piezo buzzer.
  8. Thereafter I separated the display from the circuit, so that I can solder in wires to its button contacts.

How I made a base to hold the buttons:

  1. I soldered in 3 mini push button switches to a piece of dot board, which will be used to change the settings of the watch.
  2. I connected one terminal of all 3 switches to the common contact of the watch.
  3. Afterwards connected the buttons of the watch to the individual switches.
  4. The battery plate was soldered to the common terminal of the switches and the terminal for the piezo buzzer was connected to extending wires.
  5. I also connected a wire to the alarm disconnect switch which we found out to be the button for the light on the watch.

After completing all that, I screwed the watch back in place.

Step 6: Soldering the Rest of the Components

The remaining components which needed to be soldered:

  1. I soldered in two wires to the left and middle pin of a 10K potentiometer.
  2. I also soldered in a 9 volt battery connector to the PCB.
  3. The potentiometer was soldered to the PCB as well.
  4. The alarm signal input was connected to the first thyristor and the common contact to the ground of the PCB.
  5. The alarm turn off wire was connected to the Collector of the Second Optocoupler and the Emitter was connected to Ground.
  6. Thereafter I soldered in some wires which would connect to a micro switch.
  7. I added a mini slide switch in between the pcb and the micro switch so that the feeder can be turned off when needed.

Step 7: Housing for the Components

The steps I took to install all the components into a housing:

  1. I used a plastic casing which I made the necessary openings beforehand.
  2. I inserted the servo into the necessary opening and screwed it in place.
  3. I used hot glue to stick the watch to the casing.
  4. Afterwards I screwed in the buttons of the watch to the casing (all 3 buttons seem to work perfectly).
  5. I connected the servo to the PCB, and installed the potentiometer and the slide switch to the casing.
  6. Afterwards I passed the wires for the micro switch out through the small opening near the servo, and screwed the PCB onto the casing.
  7. I fixed a plastic clamp onto the bottom cover of the casing so that the feeder can be mounted on an aquarium easily and screwed the cover shut.
  8. I placed a knob on the potentiometer so its easier to adjust it.
  9. I trimmed the wires for the micro switch and soldered it to the normally closed contacts of the micro switch.

Step 8: Container for the Food

I used a plastic container to store the food, which is to be dispensed by the feeder.

  1. I made several openings, each for different functions.
  2. I used a piece of plastic as a divider, to which I also made an opening for the food to pass through.
  3. I used hot glue to stick it to the container.
  4. I also used another piece of plastic as an adjustable cover, in order to limit the amount of food which falls out of the feeder.
  5. I used a nut and bolt to hold the adjustable cover to the container.
  6. I used hot glue to stick the nut in place.
  7. Afterwards, I stuck the arm of the servo to the middle opening of the container with hot glue.
  8. I added a nut and bolt to the opening on the edge. This will be used to trigger the micro switch.
  9. I thereafter secured in the container to the servo, using the screw provided with the servo.

Step 9: Test Run

On the intial test, the servo keeps running without stopping after one turn. So we need to adjust the bolt which is supposed to trigger the micro switch.

It seems to trigger it properly on the second test.

I added the cover of the container, and tested it again. It seems to work perfectly.

I went ahead and labelled the on off switch and the buttons which control the clock.

Turning the potentiometer, we can adjust the speed at which the servo rotates.

I added some fish food, and turned the feeder ON. Afterwards I tested out the timed feeding function. It works perfectly as well.

Step 10: How the Circuit Works

In basic terms, the watch alarm triggers the feeder into dispensing food, and the micro switch turns OFF the rotation when a full turn is complete.

The complete process is that:

  1. The watch send a pulse to the piezo buzzer which causes the sound you hear.
  2. The pulse is very small, so we use a thyristor to pick up the pulse.
  3. The pulse turns ON the thyristor allowing electricity to pass through.
  4. But the pulse turns ON and OFF rapidly (which causes the beep-stop-beep-stop.... sound), so we need a second thyristor to keep it turned ON.
  5. When the first thyristor turns ON, it turns ON both the opto-couplers
  6. The first opto-coupler turns ON the second thyristor (and this stays ON, without turning OFF until the micro-switch is pressed).
  7. The second opto-coupler turns ON the alarm stop switch (this is because if the alarm is still beeping, and the dispenser has already completed one turn, it will keep turning, since the watch keeps sending the signal. This will result in many turns rather than just one).
  8. After the second opto-coupler turns OFF the alarm, the first thyristor turns OFF as well, but the second thyristor stays ON.
  9. After the dispenser completes one full turn, the bolt which we fixed onto one of the edges will hit the micro switch, and disconnect power to the circuit (since we soldered the wires to the normally closed contact).
  10. The capacitor which we added to the circuit will give it the last kick the servo needs to go over the micro switch, even after the power is disconnected. This is needed because if there is no capacitor, the bolt will get stuck at the micro switch and keep the power disconnected.
  11. The feeding stops till the watch sends a signal once again, when the alarm is turned ON.
  12. The cycle repeats

I hope this instructable helps. Remember to Vote for it below, so we can keep making awesome projects and share with you on instructables. Stay awesome, and see you in the next project :)

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