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Attach a step-down transformer to the left side of a perfboard. Arrange 4 diodes in a diamond shape to the right of the transformer. Wrap wires around the left and right of the diamond. Use a multimeter to check the DC voltage on the wires.
A step-down transformer is a small electrical device that has wires with differing numbers of coils to lower the voltage from a supply to the output. For a simple converter circuit, look for a transformer that’s rated for at least 13 V so you can drop the input power lower. Place the transformer on a piece of perfboard, which has a grid of holes drilled into it and is used for prototyping circuits. Connect the transformer to the perfboard using nuts and bolts to secure it in place.  You can buy transformers and perfboard from an electronics supply store or online. If you want to raise the voltage, then you can use a step-up transformer instead. Diodes allow electricity to go through them in 1 direction, but they block the current from going the other way. Place the first diode at a 45-degree angle so the positive end points away from you and to the left. Place another diode next to the first one so they form a corner and the negative end points at a 45-degree angle to the right. Form the top of the diamond so the diode on the left has the negative side pointing up and the diode on the right has the positive side pointing up.  The diamond pattern of the diodes is known as a bridge rectifier and allows the circuit to transfer the positive and negative outputs of the AC signal. You can buy diodes from an electronics supply store or online. Make sure the diodes are pointing in the right directions or else the current won’t be able to flow through them. You can use hot glue to secure the diodes to the perfboard if you want, but it’s not required. Choose copper wires with differently colored insulation for the lines that the DC signal runs through. Wrap the end of 1 wire around the left corner of the diamond so it goes around both of the diode leads. Then attach the second wire to the diode leads at the right corner of the rectifier so it’s secure. Guide the wires toward the right side of the perfboard so they’re away from the transformer.The leads connected to the left and right carry the DC signal away from the rectifier. Turn your multimeter so the dial points at the “DCV” or “V–” option. Plug the leads into your multimeter and hold the pins against the positive and negative sides of the capacitor filter. The reading on the display will be the DC voltage converted from the original AC supply.You can also attach a DC-powered lightbulb to the wires on your capacitor filter to see if it lights up. If the light stays on consistently, then the converter worked.