The Nag
Pointless Electronics PE-003 · An empty box that yells at you when you close it · Reed switch, one-shot, recording module · By Onion Madder · Mess O' Pedals
There is nothing in the box. You open it, and it says nothing. You put the lid back on - the tidy thing, the correct thing, the thing anyone would do - and it yells at you.
It started as a box that screams when you open it, and that version got thrown out for being useful. A box that screams when opened is a burglar alarm; it has a purpose, it deters something, you could justify owning it. Yelling at someone for closing a lid can't be justified by anybody. There is no scenario in which it helps.
It's also inescapable, which the open version isn't. If it yelled when you opened it you could close the lid and the exchange would end. Yelling when you close it means the only way to avoid being yelled at is to leave a box open forever. That is the device's one demand and it does not negotiate.
About an hour, and it reuses the One Shot board.
Before you start
tap to expand / collapse
The box stays empty. The moment it holds anything, it becomes a thing that guards the contents, and it stops being funny. Everything mechanical lives in the base or under a false floor. What the person opening it sees is nothing.
Reed switches are glass. Don't bend the leads right at the seal - grip the lead with pliers between the glass and the bend, and let the pliers take the strain. Same rule as any glass-bodied part.
What you'll need
tap to expand / collapse
- 1× ISD1820 recording module - spot it: small blue board with a microphone can and three tactile buttons marked REC, P-E and P-L. Records about ten seconds through its own mic and drives a small speaker with no amp. The ISD1820 guide has the whole board mapped
- 1× One Shot board - spot it: the 555 monostable on 9 strips. Full layout and build on its own page. If you don't have one, build it first - this project is where it earns its keep
- 1× reed switch, normally open (RS1) - spot it: a small glass tube with two flat metal blades inside that overlap but don't touch, and a wire out each end. Hold a magnet near it and you'll hear it click. Normally open is the common and cheap kind - that's the one you want
- 1× small neodymium magnet - spot it: a silver disc, 5-10mm across, that sticks to things hard for its size. A fridge magnet is not strong enough
- 1× 8 Ω speaker, 0.5W - spot it: two terminals, no polarity to worry about at this power
- 3× AA and a holder - spot it: three cells. 4.5V sits inside the module's 3-5V window and stays there as they drain
- 1× power switch (SW1) - spot it: any small SPST toggle. It goes on the outside, for reasons that become obvious the first time you try to turn it off
- 1× a box with a lid that opens and closes - spot it: hinged or push-fit, wood, tin or plastic. Not a pedal enclosure with a screw-on backplate - the lid has to be something you'd casually close. See Choosing A Box
The whole circuit
Four connections and a magnet.
Steps 1–5 Record the yell
Do this first, on the bench, with everything loose. Keep it short - under two seconds. A long yell outstays its welcome fast on an object you'll trigger a hundred times.
| Step | Do |
|---|---|
| 1 | Connect the battery holder to the module's VCC and GND. |
| 2 | Connect the speaker to SP+ and SP−. |
| 3 | Hold REC down and yell into the microphone. Let go. |
| 4 | Press P-E and listen back. |
| 5 | Do it again until you have one you can stand hearing repeatedly. Each recording overwrites the last. |
Leave the module's oscillator resistor alone. The 470K swap from The Groaner pitches everything down into a moan - that's a different object. A nag is shrill and quick. Stock value, normal pitch.
Steps 6–10 Wire the two boards together
| Step | Do |
|---|---|
| 6 | Solder a wire from the One Shot's V_OUT to the module's VCC. |
| 7 | Solder a wire from the One Shot's G_OUT to the module's GND. |
| 8 | Solder a wire from the One Shot's OUT to the module's P-E pad. |
| 9 | Solder the battery holder's red lead through the power switch to the One Shot's +V. |
| 10 | Solder the battery holder's black lead to the One Shot's GND. |
Steps 11–15 The reed
| Step | Do |
|---|---|
| 11 | Solder a wire to one lead of the reed switch, gripping the lead with pliers between the glass and your joint. |
| 12 | Solder a wire to the other lead the same way. |
| 13 | Solder those two wires to the One Shot's IN_A and IN_B. Either way round - there's no polarity. |
| 14 | Switch on, hold the magnet against the reed, and listen. It should yell once when the magnet arrives and stay silent when it leaves. |
| 15 | Note how far away the magnet still triggers it. That distance sets your lid gap. |
Steps 16–23 Into the box
| Step | Do |
|---|---|
| 16 | Drill the speaker grille in the base or a side wall - anywhere but the inside face you'll be looking at. |
| 17 | Drill the power switch hole on an outside face. |
| 18 | Mount the reed switch in the base, close to where the lid meets it, and glue it down. |
| 19 | Glue the magnet into the lid, lined up with the reed and inside the trigger distance you measured. |
| 20 | Fit the speaker over the grille and seal round its rim with putty or glue. |
| 21 | Tuck both boards and the battery holder into the base, taped or sleeved so nothing shorts. |
| 22 | If the box has an open interior, fit a false floor over the lot so the inside reads as empty. |
| 23 | Close the lid. |
The off-board wiring
Every pad here is on the One Shot board; its own page has them drawn.
| Pad | Goes to |
|---|---|
| IN_A | Reed switch, one lead. |
| IN_B | Reed switch, other lead. |
| OUT | The module's P-E pad. Goes high for 2.4 seconds when the lid shuts. |
| V_OUT | The module's VCC. |
| G_OUT | The module's GND. |
| +V | Battery +, through the power switch. |
| GND | Battery −. |
If it doesn't work
| Symptom | Check |
|---|---|
| Yells when you open it instead of when you close it. | You've got a normally-closed reed. Swap it, or add the 1M and rewire as described below. |
| Nothing happens at all. | Power switch, then cells, then whether the recording exists - press the module's own P-E button and see if it plays. |
| The module's button works but the lid does nothing. | Magnet too far or too weak. Meter across the reed and close the lid slowly; if it never clicks, move the magnet closer or get a stronger one. |
| It yells twice, or stutters. | The magnet is passing the reed on the way in and triggering twice more than 2.4 seconds apart. Reposition so it approaches once, or take R1 up to 4M7. |
| It yells every time you pick the box up. | The magnet is sitting right on the edge of the trigger distance, so any flex makes and breaks it. Move it a few millimeters closer. |
| Thin and papery. | The speaker isn't sealed to its grille. Putty all the way round the rim. |
How it works
A normally-open reed switch closes when a magnet comes near it. Put the magnet in the lid and the reed in the base, and closing the lid closes the switch. That's a contact making, which is exactly what the One Shot triggers on - so no inversion is needed anywhere.
You could wire the reed straight to P-E and skip the board. It would mostly work. The reason it's here is that a lid being closed is a messy mechanical event - it wobbles, it settles, the magnet swings past the reed on the way in - and every one of those makes and breaks would restart the yell. The board takes all of that and emits one pulse.
Better still, the One Shot's input is edge-coupled, so a reed that sits closed under a shut lid doesn't keep retriggering. Nudge the closed box, shake it, carry it across the room: silence. It yells once per genuine closing and at no other time.
Why it yells on closing and not on opening
This is the one piece of the design that could have gone wrong, and it's worth understanding because the wrong version looks identical on the bench.
A normally-open reed closes in the presence of a magnet. Lid shut means magnet near means reed closed. Lid open means magnet gone means reed open.
The One Shot fires on a contact making, not breaking - its input is a capacitor that passes the downward step when the switch pulls the trigger node to ground. So closing the lid fires it and opening the lid does nothing at all.
If you'd wanted the opposite - the alarm version, the one we threw out - you would have had to fit a 1M resistor from the input strip to ground and wire the reed between IN_A and the positive rail instead. Then the node falls when the reed opens. Worth knowing, both because you might want it for something else and because it explains why a sensible-looking build can end up doing precisely the wrong thing.
One consequence to keep rather than fix: switch it on with the lid already shut and it yells immediately. From the circuit's point of view you just closed it. That's correct and you should leave it.
Choosing a box
It needs a lid you'd close without thinking. That rules out anything that screws shut. A hinged wooden box, a tin with a push-on lid, a plastic case with a clip, a cigar box - all fine.
Small is better than large. The joke is strongest when opening it reveals an obviously, pointedly empty space, and a big empty box just looks like it's waiting to be filled.
Don't label it. A box with nothing written on it is a box; a box marked DO NOT OPEN is an invitation and changes the whole transaction.
Things to try
- Pitch it up. The Groaner went to 470K to drag the voice down. Going the other way - 47K in place of the stock 100K - should make it faster and shriller, which is more naggish. That's below the chip's specified range and I haven't tried it, so treat it as an experiment.
- Record something quieter than a yell. A flat “really.” or a single disappointed sigh is worse to be on the end of than shouting, and it wears better over a hundred openings.
- Make the lockout long. R1 at 10M gives you eleven seconds of deafness after each yell, so rapid open-close-open-close gets you exactly one complaint and then contempt.
- Put a second magnet in the wrong place so there's one spot on the lid that triggers it early. Nobody will ever work out why it sometimes goes off before the lid is shut.
- Build the alarm version too and keep them next to each other. One yells when opened, one when closed, and between them there is no safe action.
Credit where it isn't due: reed switches and magnets have been telling on lids since the 1930s and none of that is mine. The inversion, the empty box, the boards and the words are. Build it, bend it, make it yours.