Lighting House

This circuit can be used for a flashing light transparent plastic toy. A good example is a transparent plastic house toy, thus the name of this Instructable.

The first video shows the circuit working. The second video shows a 35-second video with music and a schematic diagram.

Please read this article from beginning to end if you are going to build this circuit at home.

Components: AA battery holder for four AA batteries with a switch, AA batteries - 4, matrix board, LM747 dual opamp IC (integrated circuit), 14 pin wire wrap socket, wire wrap wire, 10 kohm resistor - 5, 22 kohm resistor - 1, 1 Megohm resistor - 1, 180 ohm resistor - 1, 1 uF polyester capacitor or two 470 nF polyester capacitors, 10 mm thickness LED.

Tools: Wire wrap tool.

Optional tools: voltmeter/multimeter.

Software: PSpice simulations software student edition version 9.1.

The circuit consists of a Schmitt trigger oscillator and a non-inverting operational amplifier.

Using a higher Farad value capacitor will increase the oscillation frequency. However, I could not find a polyester capacitor above 2.2 uF and electrolytic capacitors are not reliable. The 2.2 uF polyester capacitor was expensive. Thus I have chosen 1 uF capacitor instead. The 470 nF capacitors are cheaper. However, you will need to buy two and connect in parallel because the capacitances of parallel connected capacitors is the sum of the values of the connected capacitors.

You can google Schmitt trigger oscillator to find out how to calculate the oscillation frequency. There are many articles on this topic online.

Calculate the maximum LED current:

Saturation voltage Vsat = 0.5 V:

IledMax = (Vs - Vsat - Vled) / Rled

= (6 V - 0.5 V - 2 V) / 180 ohms

= 0.0194444 A

= 19.4444 mA

Saturation voltage Vsat = 1 V:

IledMax = (Vs - Vsat - Vled) / Rled

= (6 V - 1 V - 2 V) / 180 ohms

= 0.0166667 A

= 16.6667 mA

I used a big 20 mA LED. A typical LED needs 10 mA. Not 20 mA.

You can use a dual LM747 operational amplifier if you want to build this circuit.

I also considered using a power supply of 4.5 V. However, operational amplifiers need high voltage. They would not work well at low voltages, especially if your AA batteries are slightly discharged. If you really want to use 4.5 V power supply you will need to reduce the Rled resistor value. I did not test the circuit with a 4.5 V power supply. It might not work at all.

The C1 capacitor voltage output is similar to that of a triangle wave signal.

Simulations show an LED current of about 19 mA, similar to the predicted value of 20 mA.

I made the circuit with wire wrap. I did not use a soldering iron.

I tried making the circuit with Rf1a of 10 Megohms instead of 1 Megohms. The circuit worked and you can see it on Product Circuits YouTube and TikTok channels. However, because the simulations showed that the circuit would not work I decided the change the value of Rf1a from 10 Megohms to 1 Megohm. Operational amplifier input resistance is not infinite. Thus using a high Rf1a value might mean that the C1 capacitor would not change to a value high enough to change the operational amplifier oscillation voltage output from maximum to minimum. Operational amplifiers have manufacturing tolerances. Thus what worked for my operational amplifier might not work for all operational amplifiers.