In my apartment all of my lights are controlled via an outlet. These outlets are not connected to a light switch. As a first step towards convenience I purchased an EtekCity wireless outlet and switch. Every Friday these lights are put on a timer until Saturday night. That meant removing the existing outlet adapter and putting on one of the lovely cheap timers for the day. The timers only have a 24 hour cycle so it did not make sense to leave them on for the rest of the week. Within the timer there is also an audible mechanical clicking. There had to be a better solution.
Of course! I already have a wireless light switch. Why not somehow interface with it? A quick search on a hackaday lead me to others who have done similar, such as this and this. It was possible and not too hard.
Nixie tubes are awesome. Nixie tubes are the LEDs of the past. They were used in devices such as calculators. The inside of the tube is filled with gas, usually neon. To ignite the neon you need a high voltage, usually 150VDC or more. I plan on making a nixie clock. I've had these tubes for a while but have not had the time to play around with them. I really wanted to see the nixie in action, so I made a counter with the supplies I had on hand.
I will run through the devices and what they do, starting from the power source.
Power Source: The AC outlet is hooked to a transformer that outputs 12VDC. I chose 12VDC supply because it's perfect for driving the high voltage power supply (HVPSU) as well as the Arduino. There is a potentiometer in the schematic which I used to drop the voltage down to 5V. This is because the 74141 and its inputs are powered by 5V. Each common ground in the picture is connected to the 12VDC ground.
High Voltage Power Supply: This was purchased from All Spectrum Electronics. The input comes from the 12VDC and the output connects to the anode of the Z573M. WARNING: HIGH VOLTAGES ARE DANGEROUS AND CAN HURT/KILL YOU. If you don't know what you're doing, find someone who does before playing with high voltages.
Arduino Nano: This is where the binary count comes from. In the program I made a simple function called output which would output the number given to specific ports on the Arduino. You can view the code here.
2N2222A: The Arduino Nano outputs do not have sufficient power to drive the 74141 inputs. To make the outputs of the Arduino actually do something I had to hook them up to transistors. Each transistor is set up as a switch. There is 5V going into the collector of each transistor. When there is current going through the base it will turn on the transistor. Each base is hooked up to the outputs of the Arduino. The emitter is connected both to a 1kΩ resistor and the input on the 74141. The 1kΩ resistor is called a pulldown resistor. The pulldown resistor is used because the 74141 can not have a floating voltage. This way, when the transistor is off, the input on the 74141 will be coming from ground, which is 0V. When the transistor is turned on, the 5V will go from the collector to the emitter. The remaining voltage of 4.3 (~0.7V drop over the base of the transistor) at the emitter will be dropped over both the pulldown resistor and the input of the 74141.
74141: This IC allows you to input a number in binary format. You input the number in Binary Coded Decimal (BCD) format and it outputs in decimal format. The IC is designed to drive HV nixie tubes which have decimal cathodes. I will explain how this works a little bit more. We have 147V going into the nixie tube anode. Current flows from the anode to the cathode. Each cathode of the nixie tube connects to a pin on the 74141. Remember, you need a difference in voltage potential through a device for current to flow. So for example, when we want the number zero to display on the nixie tube, the only pin we want to have a voltage difference at is pin zero. That is why, as you can see in the datasheet, when an output is ON, it's at ~3V, all other outputs are at ~70V. Therefore the only pin with a large enough voltage drop to ignite the neon is the number zero.
Z573M: The cathodes are k0 through k9. These are all hooked to the 74141. The anode is hooked to the HVPSU through a current limiting resistor of 10KΩ. In the datasheet you can see there is a pin for IC and dp. The dp pin turns on the decimal point which is to the bottom right of the number. The IC visually does the same as dp. I'm not sure if there is any other purpose for it.