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.

Hello again.

Thank you so much again.

I have two other A Levels to work on and so will get round to getting my shopping list together soon and I will let you know. My teacher tells me we buy most of our stuff from www.kitronik.co.uk and so he would like to get as much as possible from them, but he also uses Rapid who probably have a wider range of stock.

Thankyou!!!!

 

Personally I would choose a PCB mountable relay, because you will need a PCB to mount some of the other components, such as the capacitor and resistor/s, SCR etc.

I would built the PCB using wire to board terminals in order to make it modular.

 

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.

The smaller components such as diodes and capacitors etc, we either have in school or can easily source. We have no PCB making facilities in school so will either have to source modules / pcb mounted components such as the "second" relay or use veroboard.

Are you suggesting the two channel 12v PCB mounted relay?

if so my shopping list looks like this, minus the incidentals, unless you can advise different.

What do you think? basically as before but with the dual relay board

Relay
Timer
Microswitch
Motor
PSU

Thanks again.

 

If you are using veroboard you could use ElectricSpidey's suggestion to use PCB mountable relays. (Check that their pins are on a 0.1" spacing.) Your list of parts with the automotive relay replaced by the dual relay board should be OK.

Les.

 

Here is the suggested circuit using the dual relay board.

I suggest a value of 100 uF for C2. The value of C1 will depend on how long the motor takes to start and get past the notch in the disk.
This is how it works.
When the timer contacts close C1 generates a positive pulse on the input of relay 1. This causes it's NO contact to close driving the motor past the notch. Once past the notch the motor is driven via the NO contact on the micro switch until the next notch is reached. The NC contact switches +12 volts to the positive end of C2 which causes a pulse to relay 2 input. Relay 2 is then held in via it's NO contact which also drives the buzzer. The reset button breaks the supply to the common contact on relay 2 which causes it to unlatch switching off the buzzer. Diodes D2 & D3 prevent the inputs to the relay board being reverse biased while the capacitors are being discharged. Diode D4 prevents C2 from being reverse charged if the buzzer has no been cancelled before the next dispensing time.

Les.