Egg drop - box with 555 siren alarm inside.

Discussion in 'The Projects Forum' started by cpqfe29, Mar 25, 2013.

  1. cpqfe29

    Thread Starter New Member

    Jan 30, 2010
    Daughter’s school project. Egg Drop. I am going with my tried and true cardboard box with egg suspended in pantyhose. My daughter came up with an idea with putting an alarm on her “Egg Protector 4000”. My little nerd J . She wants an alarm to sound and flash red LED’s when someone puts their hand into one of the access holes. Due to the project date of this Thursday I have no time to order parts online and am stuck with Radio Shack and components that I have laying around. I have searched high and low for information but am getting “Google eyes” and information overload.

    I researched a 555 timer siren design for the “alarm”. I built a couple on breadboards but I realize that there is no way to turn it on or off via a pin (pin two I believe). I assuming the only way to make it go on and off is to interrupt or apply power via a trigger – sensor.

    Her cardboard box is a rectangular (16L x15 Wx13h) with two access holes (6x7) cut into opposite sides on the 15x13 panel sides. There is about 4 inches on each side of the windows. You only need this information if it helps determine the sensor requirements.

    Option one:
    I was going to go with using two pairs of infrared Emitter and detectors (one for each window) but I am not sure how precise they need to lined up or if I would need two sets to cover one 6x7 window. Radio Shack # 276-142.

    Option two.
    Radio Shack # 276-135. Parallax PIR Sensor v.B. I was thinking of using one sensor mounted in the middle of the box on one side to cover the entire inside. I do not know if this is too close (low mode is 15ft compared to 30 feet high mode – I am only working with 16 inches inside the box) or if this sensor is too sensitive or problematic . I don’t need it going off with false alarms too much – master on/off switch will be used. I also need to do this without an Arduino. When triggered the output goes high. It is unbelievably hard to find information on how to use this without an Arduino –or it was overlooked.

    Dual 555 sirens built and tested. (CMOS 555 – low power from TI – regular ones available if better for this purpose)
    Led output is coming off of pin 3 on first 555 timer – then will be amplified to allow for 4- 6 red LEDs.
    Power sources are no problem. 9 volt with regulator most likely- have many 3 volt cells available.
    Four different circuits: power (1 or 2), siren trigger (1 or 2 depending), siren, and LED circuit.
    I need help with how to ‘activate’ the 555 siren.

    Does this look like I am going the simple route (Firm believer in KISS – keep it simple stupid)?
    Infrared or Parallax PIR? Or perhaps another trigger method?
    If infrared is best – is the Radio shack pair enough to cover a window? Based on any generic infrared detector circuit – what is a good way to trigger the siren? I assume it has to be via power switching to the siren circuit – but how? Relay, transistor, transistor pair, etc.
    If Parallax PIR is best – would it work in such a confined space? How to I use the output to trigger the siren. I assume it has to be via power switching to the siren circuit – but how? Relay, transistor, transistor pair, etc.

    Of course you can’t answer some of these questions because I will need to just build it and try it to see which ‘trigger’ is best. I also do not have a schematic for the 2 Dual 555 sirens that I built and tested – they work but I need to switch power to it I assume. I may be assuming incorrectly – so I can post it if needed. I have not built any of the ‘triggers’ yet simply because I am not sure how to incorporate them.

    Thank you in advance for any guidance that you have to offer.
  2. JohnInTX


    Jun 26, 2012
    I'd use the PIR. Easier than trying to align IR beams in a cardboard box. A close range should not be an issue.

    You should be able to control your 555 sirens using the RESET pins on the 555s. Pull them low to stop the sound. See Bill Marsdens's blogs here and the ebook for much 555 stuff.

    You could use a flipflop for control, another 555 maybe or 4000 CMOS depending on what you have laying around. Set it when the PIR detects to raise the 555 RESETs and allow them to run. Clear the f/f with a button to silence/rearm the alarm.

    Post some schematics if you can for specific help.

    Have fun!
    Last edited: Mar 25, 2013
  3. elec_mech

    Senior Member

    Nov 12, 2008
    Neato. I used the PIR sensor not too long ago for a project for someone else, so I can lend a hand.

    I've attached a schematic showing some hook-ups.

    First, the PIR sensor operates off of 5VDC. You can use a 7805 regulator or similar, but I decided to use a 5.1V Zener diode which RadioShack does carry.

    Second, the PIR sensor requires 4-5 seconds of warm-up to calibrate itself whenever powered on. This means its output will be high during this time, triggering whatever you have it connected to. In my circuit, I used it to trigger a couple of monostable 555 timers. I added R1 and C1 as a power-on delay. When connected to the reset pin (4) of the 555, the 555 are in reset (effectively turned off) for ~7 seconds and aren't accidently tripped while the PIR sensor warms up. This only works if the power is removed for about a minute or more so C1 can fully discharge. If you remove and restore power in under a minute, this will be useless and your alarm will go off immediately. Just something to keep in mind.

    Third, the PIR sensor is not capable of handling much current. To keep it safe, I added an NPN transistor. As shown, when the PIR is tripped, it will send a high signal to the NPN which will in turn send out a low signal.

    Fourth, the PIR sensor takes a few seconds to shut off once triggered. Alternately, it can on indefinitely if constantly triggered. Because I used monostable 555s and I did not want the 555s triggered continuously if the PIR was high for long period of time, I added C2 and R4 as an edge-trigger. This means when the PIR is tripped, the output of the NPN is a brief low pulse, then goes high and stays high until the PIR output goes from low-to-high again. If the PIR remains tripped, the output of the NPN will not change (remain high).

    I'm not sure how your dual 555 circuit works. Since it is for an alarm, I assume it is an astable circuit. I can help show you how to best connect it if you can post a schematic. If not possible, tell us how you turn it on and off.

    If you want to control your alarm time, I'd suggest adding a monostable 555 between the PIR and the siren circuit. In this way, you can trip the monostable and have the alarm go off for however long or short as you want with the ability to ignore the PIR until it resets (turns off then gets triggered again).
  4. cpqfe29

    Thread Starter New Member

    Jan 30, 2010
    Last edited: Mar 26, 2013
  5. elec_mech

    Senior Member

    Nov 12, 2008
    Just note the Zener diode is not capable of handling much in the way of current. The PIR sensor doesn't require much, so it's okay to use here. Also note, if memory serves, the Zener circuit can pull up to 30-ish mA, so be sure to cut power when not in use to conserve battery life.

    I've put together a simple interface using a couple of transistors. This does not have any timing, so whenever the sensor is tripped, the alarm will go off until the sensor output goes low. Also, note I'm not a transistor guru in the least, so if someone points out any obvious flaws in my circuit, heed their warning and I'll correct it as well. If you weren't limited by time to RadioShack, I'd suggest a logic-level MOSFET instead, but they don't sell those to my knowledge.

    If you opt to add the timing, you can add a 555 in monostable mode and add a potentiometer to adjust the timing - just use the first circuit I posted instead to connect it to the PIR. Let us know if you need any help.

    Good luck!
    forsat likes this.
  6. cpqfe29

    Thread Starter New Member

    Jan 30, 2010
    I have the PIR working and the siren circuit working on separate breadboards. I just can't seem to get them working together - yet.

    It is late so I will walk away until tomorrow and approach it with a fresh head. I will remove and rebuild the section coming off of the output of the PIR to the 555 circuit. I will likely put in the timing section if time permits.

    Thanks for the help so far! :D
  7. elec_mech

    Senior Member

    Nov 12, 2008
    If you're still having trouble interfacing the two, post a schematic showing how you've hooked the two together and we can help you troubleshoot it.

    I've put together two additional schematics on adding a timer feature and interfacing to your siren circuit. The first just ties the output of the 555 timer to the power of the siren circuit. A standard 555 can output up to 200mA and I'm assuming your siren circuit takes a fraction of that, so it should be okay.

    The second circuit is how I'd do it if you could redo the connections to the reset pins of your siren circuit. This will force the 555's into reset until a high signal comes from the timer.

    VR1 and C5 will give you a maximum on time of about 10 seconds. If you want more, then you can increase C5 or VR1. R6 is used to provide a minimum value in case the potentiometer is set to 0Ω.
    forsat likes this.