Noobie with newb questions for simple project

Hi Brian,

I'm not sure it is as straightforward as you suggest : ( The devil is in the detail. At a high level,  the pseudocode is simple:

while(1)
{
  result=readTag();
  if(result)
  {
     lifting_mechanism=1;
  }
  if (photosensor==1)
  {
     alarm=1;
  }
  else
  {
    alarm=0;
  }
}

In practice, you'd need to decide when to set the lifting mechanism output back to zero, and find a way of getting a reliable photosensor output in all lighting conditions, and decide how often you wish to scan the imputs and use a sleep or wait type of instruction. In any case, the pseudocode meets the requirement as you stated, I'm just suggesting that the system will be more complicated than that. There are also better ways to code the solution, but is a bit more complicated - if you explore the topic of 'interrupts' you'll see some ways to modify the code so that it doesn't need to scan/poll inputs.

Perhaps take a look at this RFID tutorial:

Tutorial 12 for Arduino: RFID Card Reading

It's for a door lock however it covers a lot of the elements your project requires, namely the reading of a RFID tag, operating a motor, playing an audio notification. There is a button input but in this case it is attached directly to the RFID reader enable pin rather than the Arduino so you may want to take a look at this other tutorial on using a LDR sensor with an Arduino:

Tutorial 04 for Arduino: Analog Inputs

Thank you guys!! I will look into all of the info that you guys provided so far.

I think I have actually gotten away from the rfid portion in my project as there would be too many limiting factors: mainly my transporter and package are huge metal structures which will throw the reliability of rfid too out of whack I think. Also, I found a novel way to lower my transporter using a sensor instead.

The only task I need to figure out now is how to have my arduino activate a relay for a certain amount of time when another sensor is activated for a certain amount of time. Kind like: if this for x seconds, then this for y seconds...

Hi Brian,

It is not clear to me whether your issue is firmware or hardware

The only task I need to figure out now is how to have my arduino activate a relay for a certain amount of time when another sensor is activated for a certain amount of time. Kind like: if this for x seconds, then this for y seconds...

However, here are some thoughts:

• If it is determining how to get an x value for a given y value then you can use least squares regression or set up a table and interpolate.  An internet search will turn up hits for both.  Do a search for "delay without blocking" to understand the proper way to implement a time delay.
• If it is hardware and using a relay then do a search for "Arduino relay" and you will get numerous hits.  The quality of them can be quite bad and even dangerous is you are controlling mains.  I cannot recommend one without knowledge of what you are doing and what relay you will use.  Presuming it is low voltage though you can use an Arduino shield or to build your own - look for a tutorial that includes a transistor to control the relay and a flyback diode to protect the transistor - SparkFun has one I think.  If it is mains then I would stick with something like a PowerSwitch Tail if you are in the USA.  I am sure there are equivalents in Europe and other parts of the world.

Frank

Updated suggestion for mains relay in USA:  https://www.adafruit.com/product/2935

Frank

I’m not exactly sure which problem I have either!!

I’m pretty sure I have the hardware down:

I have an Arduino Uno and I will be using a 4 channel arduino relay shield with relays capable of handling 24v dc.

What I have going on is a transporter with a lift on it. The lift is powered by a 24v motor that is operated by an up/down pendant station. The transporter will be carrying a package that is centered in the lifting mech via a photo reflective sensor which activates a buzzer when the load is centered.

What I’m trying to accomplish is that when the load is centered (the sensor is activated and the buzzer is going) the arduino will recognize the sensors as activated and start a timer that would trigger the relay shield to activate the up switch on the pendant station.

There is an outline of how to implement a delay without blocking here:  https://www.arduino.cc/en/Tutorial/BlinkWithoutDelay .  Blocking means that nothing else can be done while the instructions are carried out.  To implement it with your example you could test to see if the load is centered.  If it is, then have a variable (say activate) that is made true to turn on the relay for the desired amount of time (the constant interval in the linked code).  The variable activate is equivalent to ledState in the linked code.  Make the variable activate false to turn off the relay at the end of interval.  The code will continue to loop throughout and you could continue to monitor if the load is centered for example.

I should probably say HIGH and LOW instead of true and false.

So what bit do you need help with as it sounds like you've got most of it figured out  ?

What is the delay for ? a load settling time or time to allow someone to get out of the way perhaps ? It sounds like there could be a number of safety issues to be considered here with this project depending upon what sort of lifting equipment you are trying to control.

Once the sensor is activated, you can capture the current system time to a variable.

timer_start_time = millis();

https://www.arduino.cc/reference/en/language/functions/time/millis/

(note that the system timer overflows after around 50 days so you need to consider that if the system won't be reset within that period as millis() will jump back to zero.)

Each time around the main program loop then simply test the current system time against the stored system time with the required delay time added to it to see if enough time has elapsed yet

if ( millis() >= timer_start_time + delay_time )

If it has, then trigger the relay shield to start the lift, and if not do nothing and just loop round again.

You also probably need to consider what happens if the sensor is deactivated whilst the timer is under way. You probably want to be checking for that in each cycle of the loop and stop and reset the timer until the sensor is reactivated again.