Ok so I have ripped out a circuit from a toy I found and what it does is the when someone walks in front of the sensor it gives off a slow ac current at about 1.78 volts per second. Now I want to get this up to 4.5 volts. Dc or ac I don't care but it has to power 2 very large leds. Any thing will help but please try and keep the cost down,thanks.
Run the signal into a voltage comparator, the comparator can drive the signal to +5/0V for you.
That 5V can then be used to drive a transistor or something to control the LEDs.
See the LM358D part on the top left of the Uno Schematic as an example, where Vin/2 is compared to 3.3V.