Recently I had seen a few products that used the power of the greeting card and make it into a malicious device that repeats itself forever (or at least till the battery dies.) The version I have hacked today involves removing the greeting card batteries and replacing it with a 9 volt and adding a 555 timer chip to replay the sound continuously.
Step 1: Gather Supplies
For this build we will need-
Musical Greeting Card
9v battery clip connector or create one from a used 9v
555 Timer/ NE555P Chip- NE555P Chip
The next items can vary depending on length of song/sounds. See step 2 to determine your resistors values.
320kohm resistor - R1 in schematic (I used a 100kohm and a 220kohm in series. Make note this is 320Kohm / Kiloohm.)
22kohm resistor - R2 in schematic (Make note this is a 22 Kohm / Kiloohm.)
100 ohm resistor - R3 in schematic
100uF Capacitor - C1 in schematic
Step 2: Disassemble the Card and Find Resistor Values.
Next we remove electronics from the greeting card.
Now with the electronics accessible we need to determine the length of time the music plays for. Pull the tab and use stop watch on a phone or http://www.online-stopwatch.com/ to find out how long the music is actually playing for, the length of time this plays for determines the capacitor and resistors values. So for my card the music song played for approximately 22 seconds.
Next we visit http://www.bowdenshobbycircuits.info/555.htm and replace the calculators values to determine our resistor values, this calculator is in Milliseconds so for 22 seconds I need to get a T1 value of around 22,000. So R1 is Resistor1, I used 320K Ohms, R2 I used 22K Ohms and the Capacitor came out to 100uF. This made my 555 circuit turn on for 23.700 seconds (this is T1 or time on) and T2 is for 1.524 seconds, (T2 is our off circuit so it will shut off for 1.5 seconds.) As you can see there will be around a 2-3 second delay between replays. You can play with the resistors and capacitor values to reach optimal replay times for your greeting card.
Step 3: Determine POS/NEG, Remove the Batteries, and Rewire the Circuit.
Now we need to find negative and positive sides of the card circuit. First we will remove the plastic which activates the trigger and then we let the music finish playing. The easiest way to find the points we are looking for is the take a wire and connect the two sides for a second, you should hear the speaker start to replay the music when you touch the Positive and Negative side for that second. Now test these two points with a multi-meter to find which is positive / negative side. The important this is to find the correct sides and label them Positive and Negative for later. Now we remove all the batteries from the circuit and replace the holders back in place and add our positive and negative wires. We want to put the negative anywhere we have a good solder point. The positive side is going to be a little more tricky. We want to use the switch on the card to activate our new battery. So we need to break a connection, follow your positive wiring till you find a easy solder location and a way to cut a connection. On mine I found a small pad and could easily cut the trace of the circuit board, keep in mind this will be activating our circuit so it needs to be connected to the big black blob of the card.
Step 4: The 555 Circuit.
Now we need to wire the 555 Circuit, take special note and care to which is PIN 1, it will be closest the the half moon or it will have a dot close to it on the chip itself. Also take note - WIRING SCHEMATIC IS NOT THE CORRECT ORIENTATION OF THE 555 CHIP ( picture with black back ground ) AND IS SETUP TO MAKE THE SCHEMATIC EASIER TO READ AND UNDERSTAND. Please use the black and white pin out of the 555 chip when connecting wiring.
Basically what we are doing in removing the power source from the
greeting card circuit and replacing it with our new 555 timer circuit and 9 volt. This circuit sends power to the card for 23.70 seconds (T1) and then switches off for 1.5 seconds (T2) and constantly cycles the 23.7 seconds on and 1.5 seconds off. Thus causing our greeting card to reset every 25 seconds or so.
So to help with the setup/wiring of the chip I have found a walk though on youtube that might help, he does use a few different components but as long as you use our resistors and capacitor it is exactly the same setup. Instead of the potentiometer Make sure to use the resistor R1 in my case it was 320K Ohms.
Step 1. With the chip in hand we can cut and remove PIN 5, it is unused in this circuit and can be removed if it is in the way.
Step 2. First to wire this circuit we first need to take PIN 1 and wire it to the ground. Wire this to the Negative side of the greeting card circuit and the Negative side of the 9 volt Battery Clip.
Step 3. Next take the Negative side of the capacitor C1 (side with a white line on it) and wire it to PIN 1 and wire the other side to PIN 2.
Step 4. Now take a piece of wire and run it from PIN 2 to PIN 6 and connect the two.
Step 5. Next take R2 / in my case 22K Ohm resistor and wire it from PIN 6 to PIN 7.
Step 6. Now take R1 / 320K Ohm resistor (100k Ohm and 220K ohm in series) and wire it from PIN 7 to PIN 8.
Step 7. Take a piece of wire and connect PIN 8 to PIN 4.
Step 8. Connect PIN 8 to the positive battery wire coming from the greeting card circuit that is after the greeting card switch.
Step 9. Attach R3 / 100 ohm resistor to PIN 3 then to the part of the greeting card circuit that we cut the trace next to that is closet to the black blob. This connection sends the power to the card for 23 seconds.
Note- The Voltage coming from the Pin 3 is around 8.5volts when I was testing. One of my greeting cards had no trouble playing at this voltage, yet another one was making nothing but a hum so I added a led to reduce the voltage. If you have trouble, try adding the positive side of an led to Pin 3 and negative to the ground and see if this helps.
Step 5: Now Add Your Battery.
Now all that is left is to add the battery to the circuit. I took my completed circuit from the bread board to perf board. Then hot glued it to the 9volt battery. The only thing left to do is pull the tab and let the Happy Birthday song go on forever.