Hey,

Firstly i'm new to the forums and very new to electronics.

I'm seeking help with a project which has been driving me crazy the past week.
Any help or advice will be greatly appreciated. Thanks in advance.

Here's the situation:
Goods which are delivered to a warehouse are off-loaded from lorries by hand, and then transferred to other locations in the warehouse to be stored.

1. I have to create the delay using the capacitor and reistors.
2. I have been supplied with a DPDT 8 pin 12v pcb mount relay (which i have to use to switch the polarity of the DC motor to reverse it)
3. At least one discrete logic gate
4. Suitable light cues.

I have attached the a flow chart and circuit to be modified.

 

A datasheet for the specific relay you have been given will be needed to determine a time delay for the motor start-up.

what means will be used to determine when the lorrie is ready to be dispatched?
timed interval, weight sensor, timed object loading suspension interval, object height sensor,

what means of stopping the lorrie will be employed at the receiving station?
timed interval, photocell, weight sensor,

edit:
The suitable light cues? for incoming lorrie, warning that lorrie is departing, lorrie departed, timing countdown for lorrie departure or arrival?

 

i have attached the datasheet for the relay i've been given.

- A pressure switch or pressure pad will be used to determine departure (there is no defined weight)

- As for stopping the lorrie, just a limit switch or a micro switch

- With the light cues i wanted to try a green LED for departing, red LED for 10 sec delay and then green again for returning.

 

Is this a project that HAS to be done with discrete components or can a PIC be used?

The main issue that is staring us squarely in the face is the relay, once de-energized, is going to slam the motor into the opposite direction.
Power will also need to be interrupted from the battery to the relay contacts to stop the motor for the 10 second delay.

Another issue is if the relay is the FRT2S-B-S-DC12V, 34,700uf of capacitance will be required to keep the relay energized for the 10 seconds of delay.
10,500uf of capacitance will be needed if the relay is FRT2S-H1-S-DC12V.

Will it be acceptable to use transistors to create a delay (and lessen the capacitor count) or is that not permitted?

Lighting the LEDs will be no issue.


edit:
all in all, this should be an easy task but we need some clarification.

the flow chart states we need to detect the loaded and unloaded conditions of the lorrie. Are we to assume that the pressure switch/pad at the unloading end (normally closed when unloaded) is set to trigger when the lorrie is fully unloaded - and the pressure switch/pad at the loading end (normally open when unloaded) is set to trigger when the lorrie is loaded to its full weight?

Is this a hypothetical project you are working on or does it have a practical application?

Do we need to consider the mass of the lorrie and its load to calculate ramping the speed down before stopping?

 

The project requires discrete component

The relay reads FRT2S-S if it helps in any way.

Yes transistors can be used, there has been no restrictions set on what can’t be used, although i would like to incorporate the things i have covered so far (resistors, transistors, capacitors, relays, diodes)
I was given the equation T=RxC to figure out the delay time, which i figure is Delay Time = Resistance multiplied by Capacitance. (is this true?)

“the flow chart states we need to detect the loaded and unloaded conditions of the lorrie. what components are at our disposal to achieve that. Or is the sky the limit?”

I have a few momentary switched (push-to-make) in my collection so i would like to use those

“Or do you just need the lorrie to go back and forth with a 10 second wait at each end and LEDs to display the state of movement?
Is this a hypothetical project you are working on or does it have a practical application?”

It is a practical application, although there is not going to be any vehicle, so mass, actual load etc does not need to be taken into account. It will just be a demonstration on the circuit, focusing on the delay, working of the motor, LED’s and switches.

 

is the: "At least one discrete logic gate" a mandatory requirement?

edit:
we will need to interrupt the motor supply for the delay. Will another relay be available?

 

Yes, the logic gate is a requirement. With a logic gate, is there a specific configuration for each or can it be an AND, NOT etc as long as it performs their specified function?

Another relay can be used, yes.

Thanks for all your help VoodooMojo =D

 

not a problem...
give me a bit to draw this up
its half past midnight here now, I will post in the morning (mine)

 

Not a problem.

 

I think I remember why I loved my first Parallax!!!

This is the best from recollection of a 10 second delay stop before reversal. The values of components are not listed.
I am on the road this week and the company lap-top does not have LTSpice or any other simulator/drawing program for that matter. Except for MSPaint.
This is a variation of a theme that I used to animate statues and figurines before the advent of microcontrollers.

I am not sure how long of a run your lorrie needs but the R/C timing circuits will need to be calculated accordingly.
If not on the money, it will not function properly....

this is phase 1 and this circuit will need tweeking I am sure.
It has been awhile.

the logic gate, LEDs and other delays are yet to come, but not till I get back home to my comfort zone.

This is the best from the top of my head I could do only using relays and a few discretes.


Important to note that the motor (lorrie) will need to be wired to move into the direction of limit switch 2 to trigger the correct sequence. If it moves toward LS1, reverse the wiring at the motor.

Please feel free to comment and offer improvements.