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School technology project difficulty

Forever Learning

Apr 11, 2017
2
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Apr 11, 2017
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So for my school technology project i decided to create a puzzle box that worked like this:
The overall shape was a cube, but the top face of the cube had two translucent acryli c panels, with one having a lightbulb symbol etched on the underside (Panel A), and one with a question mark etched on the topside (Panel B); the purpose of this was for an LED to be placed under Panel A so that when it illuminated, the lightbulb symbol could be seen, and under Panel B a LDR would be placed, so that the question mark on Panel B would already be seen, causing the person who was trying to open the box to be provoked into thinking that the light must be transferred over to Panel B in order for something to happen.

Therefore, the person trying to open the box would need to shine their phone light or something similar, and this would allow the current to flow from an internal 9 volt battery to a solenoid with a spring on its rod, and so how this mechanism worked was that since there is a spring on the solenoid, the rod is normally inside a drilled hole in a spring loaded drawer (preventing the drawer from coming out of the side of the box), but when the solenoid retracts when it receives the 9 volts it needs to operate, it comes out of the drilled hole, causing the drawer to spring out.

The problem is: the actual circuit board that houses for example the variable resistor to allow me to adjust the light needed by the LDR to allow optimum current flow leeches some of the power from the 9 volt battery, so the solenoid wont work without another power source, and i dont want to do it with the mains electricity, as it would prevent the mobility feature of the box. My teacher suggested that i use a 5 amp SPDT 24VDC relay that has a 6 volt coil, so that i can have another battery snap with another 9 volt battery directly connected from the relay to the solenoid, so that when the relay recieves enough power, the separate 9 volt source will be 'activated', and the solenoid will function.

It is the actual circuit that i'm pretty much useless at, i just know what some of the components are called and vaguely what they do, so any help with that would mean literally everything to me, as it determines my final grade.

The components that i have as of now:
9v battery (2)
Push to make switch (for led section of circuit)
9v solenoid
5amp 24vdc relay with 6v coil
CBC 548B (npn transistors)
Variable resistor (dont know what kind)
LDR
Average sized LED
Resistors (2)- one for LED part of circuit, and one for LDR part for circuit.
 

shrtrnd

Jan 15, 2010
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Jan 15, 2010
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Your teacher's idea was a good solution.
Are you saying that you don't know how to build what he told you that you should try?
What's the possibility of just using two 9V batteries in parallel to increase your current flow to drive the solenoid?
 

Forever Learning

Apr 11, 2017
2
Joined
Apr 11, 2017
Messages
2
Your teacher's idea was a good solution.
Are you saying that you don't know how to build what he told you that you should try?
What's the possibility of just using two 9V batteries in parallel to increase your current flow to drive the solenoid?
Thanks for the reply, yes, you are 100% right in that i dont know how to build what he suggested. Ive got an almost complete schematic that ill attach here. As seen, when the lux (light) level increases, the power flows to the relay, which should therefore activate the second power source. I think i know the circuit, just dont know how to make it practical.
 

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Last edited:

Arouse1973

Adam
Dec 18, 2013
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There is another trick you can do without a relay. Place a small value resistor in series with the solenoid which will limit the on current. Then place a large electrolytic capacitor across the solenoid coil. The capacitor gives the initial energy to the coil on switch on and then the resistor holds it on. Not sure on the values as I don't know what solenoid you are using. I have used the many times for driving relays.

Thanks
Adam
 
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