Auto Pill dispenser / Pet Feeder Project

Thread Starter

Crakkers

Joined Feb 2, 2017
19
As to the elecronics…

24 hour timer…provides a pulse to 2 SCRs
One SCR turns on the motor.
One SCR turns on the buzzer.
Whatever method chosen to detect position shorts the motor SCR stopping the motor.
The buzzer continues to buzz until the pill taker presses a button. (shorting the buzzer SCR)

I think a micro switch would work well, and possibly a reed switch and magnets.

SCR - Thyristor?

One issue we do have is that ideally we need to use project boards as we have no PCB making facilities :(

I would look around on Amazon and such to find a 24 hour timer that can be used with the low voltage that you will use to drive the motor.
 

ElectricSpidey

Joined Dec 2, 2017
2,880
https://www.allaboutcircuits.com/textbook/semiconductors/chpt-7/silicon-controlled-rectifier-scr/

The 24 hour timer really is the key to this project, it needs to provide some sort of external “switch” that is momentary in nature, that being it doesn’t stay engaged during the entire motor movement period, there is a slim possibility that you may need to use some additional circuitry between the timer and the SCRs, if you can’t find one that fits the bill.

This could be as simple as a capacitor, as long as the timer resets before the timing period.
 

LesJones

Joined Jan 8, 2017
4,226
I was thinking of a digital plug in timer but the mechanical one should work just as well. (Except the digital one will keep track of time even when mains power is lost for up to a few weeks. But that probably does not matter for your application.)

Les.
 
I did a filter wheel for a monochometer. 4 positiions. relatively easy. I had 2'x2" filters. The wheel was 1/4" thick.

I used a 24 VAC synchronous motor from Hurst. I had a roller microswitch along the edge. I had 4 notches where I wanted the motor to srop.
the synchonous motor stops quickly, RPM depends on frequency.

You would "bypass" the switch briefly to cause it to rotate and it would stop automatically at the next position. I was able to detect "moving/stopped"

For position sensing, You can get screw in magnets. For 4 positions, I needed 2 bits, from 2 hall effect sensors. The polarity has to match.
8 positions would need 3 bits. You do have to check for stopped first, before reading the sensors.

You may not even have to know the position,
 

AnalogKid

Joined Aug 1, 2013
11,196
Try this for zero manufactured electronic circuits and zero code - five purchased products and some wires.

1. digital lamp timer plugged into the wall, programmed to come on every day from 8:00 am to 8:01 am.

2. surplus synchronous motor (AC motor and reducing gear train in one unit). This turns the turntable.

3. One limit switch (sometimes called a microswitch). This is rated for AC line voltage operation. The switch gets pushed by an index bump on the underside of the turntable when a pill compartment is centered under the window opening.

4. 555 Timer module with a relay output from ebay, adjust to make a 0.5 to 1.0 second pulse. Precise timing is not important.

5. wallwart to power the timer. This can have a 5 V or 12 V DC output, depending on which timer module you use. Any old USB wall wart or battery charger will work.

The relay NO (normally open) contacts are wired in parallel with the switch NC contacts. The contact pair are in series with the motor. This is plugged into the lamp timer along with the wall wart.

Assume the starting position is with one bay centered under the window. The switch is depressed so its contacts are open, and the timer module is off so its contacts are open, so the motor is unpowered.

At 8:00 am. the lamp timer applies power to the system. The wall wart wakes up and powers the timer module. The timer module's relay contacts close for 1/2 to 1 second. This is long enough to have the motor turn the turntable far enough to get the index bump off of the switch. When that happens, the switch contacts close to keep the motor running after the timer module's contacts re-open (in one second). Now the motor keeps running until the next index bump hits the switch, removing power from the motor. After 1 minute, the lamp timer removes power from everything until tomorrow.

You'll also need a 3-position terminal block and a line cord. I know the distributors and surplus shops in Ohio, but not in the UK. Someone "over there" can advise on components.

AND, have someone check your work, like a technician at a small appliance repair shop or someone else who is familiar with AC power wiring practices.

ak
 
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AnalogKid

Joined Aug 1, 2013
11,196
ummm ... forgot about that. OK - try this:

ebay SPDT relay module, piezo beeper, and a SPST pushbutton switch. The beeper is connected to the DC source through the relay NC contacts, and the coil is connected to the DC source through the NO contacts in parallel with the beeper button. Reprogram the lamp timer so it is on for 23 hours 59 minutes every day. At 7:59 am it turns everything off (which releases the beeper relay), and at 8:00 am. the system is re-powered. This turns on the beeper until the beeper button is pressed, which latches the relay coil on and turns off the beeper.

ak
 

Thread Starter

Crakkers

Joined Feb 2, 2017
19
I was thinking of a digital plug in timer but the mechanical one should work just as well. (Except the digital one will keep track of time even when mains power is lost for up to a few weeks. But that probably does not matter for your application.)

Les.

Hi, yes i understand that. i would go for the digital one, like the 12v suggested. Thanks

I did a filter wheel for a monochometer. 4 positiions. relatively easy. I had 2'x2" filters. The wheel was 1/4" thick.

I used a 24 VAC synchronous motor from Hurst. I had a roller microswitch along the edge. I had 4 notches where I wanted the motor to srop.
the synchonous motor stops quickly, RPM depends on frequency.

You would "bypass" the switch briefly to cause it to rotate and it would stop automatically at the next position. I was able to detect "moving/stopped"

For position sensing, You can get screw in magnets. For 4 positions, I needed 2 bits, from 2 hall effect sensors. The polarity has to match.
8 positions would need 3 bits. You do have to check for stopped first, before reading the sensors.

You may not even have to know the position,
You lost me here - sorry

Try this for zero manufactured electronic circuits and zero code - five purchased products and some wires.

1. digital lamp timer plugged into the wall, programmed to come on every day from 8:00 am to 8:01 am.

2. surplus synchronous motor (AC motor and reducing gear train in one unit). This turns the turntable.

3. One limit switch (sometimes called a microswitch). This is rated for AC line voltage operation. The switch gets pushed by an index bump on the underside of the turntable when a pill compartment is centered under the window opening.

4. 555 Timer module with a relay output from ebay, adjust to make a 0.5 to 1.0 second pulse. Precise timing is not important.

5. wallwart to power the timer. This can have a 5 V or 12 V DC output, depending on which timer module you use. Any old USB wall wart or battery charger will work.

The relay NO (normally open) contacts are wired in parallel with the switch NC contacts. The contact pair are in series with the motor. This is plugged into the lamp timer along with the wall wart.

Assume the starting position is with one bay centered under the window. The switch is depressed so its contacts are open, and the timer module is off so its contacts are open, so the motor is unpowered.

At 8:00 am. the lamp timer applies power to the system. The wall wart wakes up and powers the timer module. The timer module's relay contacts close for 1/2 to 1 second. This is long enough to have the motor turn the turntable far enough to get the index bump off of the switch. When that happens, the switch contacts close to keep the motor running after the timer module's contacts re-open (in one second). Now the motor keeps running until the next index bump hits the switch, removing power from the motor. After 1 minute, the lamp timer removes power from everything until tomorrow.

You'll also need a 3-position terminal block and a line cord. I know the distributors and surplus shops in Ohio, but not in the UK. Someone "over there" can advise on components.

AND, have someone check your work, like a technician at a small appliance repair shop or someone else who is familiar with AC power wiring practices.

ak

WOW, I think I follow that. Is this very similar to lesjones idea?

Thanks for help so far. As a complete beginner with electronics its all a bit difficult to follow, especially without a sketch. I keep alt-tabbing to google to look things up - wallwart - never heard of that before!

Lesjones. My teacher tells me he lives maybe not far from you and would be quite happy to meet for further explanations. Any chance?
 
Last edited by a moderator:

Thread Starter

Crakkers

Joined Feb 2, 2017
19
Lesjones.Project.jpg

is this what you mean?

So the 9V motor supply goes via a micoswitch that is on when the switch is pressed (outside the notch) When the disc rotates the micoswitch falls into the notch and switches the motor off. Once every 24 hys as controlled by a 12v timer this switches the motor on for sat 6 seconds or what ever it takes to bump the disc fwd to re-engage the microswitch. It this point the microswitch takes over and drives the disc to the next notch at which point the disc stops. 24 hours later the system repeats.

My only question, if this is correct......wont the motor be getting two lost of power at the same time for a short period - when the timer and microswitch are on togther - and will this blow the motor?
 

LesJones

Joined Jan 8, 2017
4,226
You diagram shows that you understand the slotted disk concept. Your wiring is not quite right. The NO (Normally open.) contacts on the timer should be connected directly in parallel with the micro switch IF you could get a timer that would give a short enough pulse. In practice I don't think you will get one that will switch on for less than one minute. (Which would probably drive the motor for more than one seventh of a rotation.) You would need to convert the off to on transition of the timer output to a short pulse. A small relay and capacitor is probably the easiest way for you to do that. (There are many other ways to do that.) Here is a very rough diagram of how to connect the parts together.
150919.jpg

I would suggest starting with C1 being about a 100 uF electrolytic capacitor and R1 about 10 K. The charging current of the capacitor will cause the relay contacts to close for a short time. This should be long enough for the notch to move away from the micro switch. The buzzer is driven with a small SCR that is also triggered to the ON state when the timer contacts close. (Via the 100 nF capacitor.) The SCR remains conducting (Driving the buzzer.) until the NC (Normally closed.) contacts open when the reset button is pressed. If a mains plug in timer was used it would have to be set to give an output for just less than 24 hours so the power remained on to drive the buzzer. When the timer switched off capacitor C1 would be discharged. when it switched back on it would cause the pulse to be generated to initiate the movement of the disk.
I hope I have explained it clearly enough. For the mains plug in timer version there would be no 12 volt timer and the two wires that went to it's contacts would be joined together.

Les.
 
The disc would have 1/2 circle notches. A 12V motor may over-run. There are ways to fix that.

I used a geared motor like these http://www.hurst-motors.com/aabgeared.html in 24 VAC.

So, you arrange the microswitch to stop the motor when it's in the groove. To start the motor, you bypass the microswitch with another switch in parallel. Either you can time it, or detect it before releasing the "bypass".

24 VAC geared synchronous motor saves a lot of headaches., but doesn't work well when the power fails.
 

Thread Starter

Crakkers

Joined Feb 2, 2017
19
You diagram shows that you understand the slotted disk concept. Your wiring is not quite right. The NO (Normally open.) contacts on the timer should be connected directly in parallel with the micro switch IF you could get a timer that would give a short enough pulse. In practice I don't think you will get one that will switch on for less than one minute. (Which would probably drive the motor for more than one seventh of a rotation.) You would need to convert the off to on transition of the timer output to a short pulse. A small relay and capacitor is probably the easiest way for you to do that. (There are many other ways to do that.) Here is a very rough diagram of how to connect the parts together.
View attachment 186255

I would suggest starting with C1 being about a 100 uF electrolytic capacitor and R1 about 10 K. The charging current of the capacitor will cause the relay contacts to close for a short time. This should be long enough for the notch to move away from the micro switch. The buzzer is driven with a small SCR that is also triggered to the ON state when the timer contacts close. (Via the 100 nF capacitor.) The SCR remains conducting (Driving the buzzer.) until the NC (Normally closed.) contacts open when the reset button is pressed. If a mains plug in timer was used it would have to be set to give an output for just less than 24 hours so the power remained on to drive the buzzer. When the timer switched off capacitor C1 would be discharged. when it switched back on it would cause the pulse to be generated to initiate the movement of the disk.
I hope I have explained it clearly enough. For the mains plug in timer version there would be no 12 volt timer and the two wires that went to it's contacts would be joined together.

Les.

WOW, Ok I think I am beginning to get this.

I guess the next stage is to model this with breadboad etc one I've manged to source the kit.

Would these be ok for the main bits??

Relay
Timer
Microswitch
Motor
PSU

Thanks so much so far!!!!!
 

Thread Starter

Crakkers

Joined Feb 2, 2017
19
hello Lesjones.

Any chance of checking my shopping list, as detailed previously with links, before i spend my paper round money?

Thanks so far!
 

bertus

Joined Apr 5, 2008
22,303
Hello,

I would make the notches more fluid.
I have drawn an idea in the top notch:

Crackers_Project_comment.jpg
When there are no sharp edges, the microswitch will not get stuck.

Bertus
 

LesJones

Joined Jan 8, 2017
4,226
I think this post probably should be classed as homework help. In that category we do not answer the question, We just give clues and point out errors in the posters reasoning. We have suggested a simpler method than your original stepper motor idea. (Which would have also worked but would be more complex.) I don't know what subject this project is related to but my best guess would be the electrical part of physics. So if you are designing this unit to show your knowledge of the subject you would have to show what calculations you have done to select the components. The motor looks about right but the information does not say how much current it takes so you do not have the required information to select the relay and microswitch contact ratings. The motor looks about right assuming my vision of the rotating disk with the tablets on being somewhere between about 50mm and 150mm diameter. (I think I would have chosen a motor that was a little faster as it will take about 3 seconds to move from one position to the next. This does not really matter for your device.) I don't think the relay is a good choice as the coil will be quite a low resistance as it is designed for use in cars. This would require quite a large capacitor to generate the required pulse. There are some miniature relays on Ebay with a reasonably high coil resistance that would be a better choice. (I noticed one that was mounted on a board with screw connections that also looked like it had a driver transistor.) If you are given the shopping list and all the build details as you will not learn anything.

Les.
 

Thread Starter

Crakkers

Joined Feb 2, 2017
19
I think this post probably should be classed as homework help. In that category we do not answer the question, We just give clues and point out errors in the posters reasoning. We have suggested a simpler method than your original stepper motor idea. (Which would have also worked but would be more complex.) I don't know what subject this project is related to but my best guess would be the electrical part of physics. So if you are designing this unit to show your knowledge of the subject you would have to show what calculations you have done to select the components. The motor looks about right but the information does not say how much current it takes so you do not have the required information to select the relay and microswitch contact ratings. The motor looks about right assuming my vision of the rotating disk with the tablets on being somewhere between about 50mm and 150mm diameter. (I think I would have chosen a motor that was a little faster as it will take about 3 seconds to move from one position to the next. This does not really matter for your device.) I don't think the relay is a good choice as the coil will be quite a low resistance as it is designed for use in cars. This would require quite a large capacitor to generate the required pulse. There are some miniature relays on Ebay with a reasonably high coil resistance that would be a better choice. (I noticed one that was mounted on a board with screw connections that also looked like it had a driver transistor.) If you are given the shopping list and all the build details as you will not learn anything.

Les.

Hi again.

The course I am following is a product design course and has nothing what so ever to do with physics or electronics. I have checked a few things with my teacher about how i am going about it.

Its fine for me to be told what components to buy - this is not cheating as I can use bought in modules to dive the system. Mt main task is to design the prototype product that fits around the system. In contrast if I was doing a systems and control or electronics or even an applied physics course i would be concerned purely with the system and not the product. A Level courses have been rationalised in recent years in that pupils specialise in a field; electronics, product design etc. So it is absolutely fine for me to find out from a 3rd party what I should buy. This is classed as primary research and very much encouraged as it shows my initiative in being able to seek advice and act upon it. Indeed all the screen shots from this thread will go into my folio as evidence for this section for the examiners to see.

I don't have the time or funding to buy components or the time to play with them to see if they work or not. As I have admitted, I know nothing about this aspect of work and its theory does not form part of my course.

I really do thank you so much for the help and support so far - I seriously do. But if you could see your way of suggesting specific components I be so grateful and less stressed about making a trial first system as I am aware that time is ticking away for me.

I hope this clarifies thing a little.

Thanks again.
 

LesJones

Joined Jan 8, 2017
4,226
I think the second relay is the best option for you as it is easy to mount and has screw terminals. You could also consider getting the board with two relays and use the second one to provide the latching function for the buzzer. (That I used the SCR for in post #31.) I suggest that you buy i few different value capacitors as it is not possible to calculate the pulse time and the pulse will probably need to be longer than I first imagined as the motor is quite slow so it will take some time to move away from the notch. I suggest a 100 uf, 470 uF , 1000 uf and a 2200 uf capacitor. If you decide to use a relay in place of the SCR then you won't need the 100 nF capacitor but you will probably need a few small diodes such as 1N4118 or 1N914. Let me know which option you want to use to latch the buzzer before placing the order so you can try to get all the electronic components from the same supplier to save on postage.

Les.
 
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