Understanding Mohit Bhoite's Seven-Segment Counter Sculpture

Freeform electronics sculptures from Mohit Bhoite always capture attention. Ironically, these beautiful PCB-less circuits come from a person who designs PCBs as a day job! Regardless, gorgeous circuits that are also functional desire admiration. Bhoite's latest piece is a counting seven-segment display powered by a 50 farad capacitor! While admiring it, we could not stop ourselves from realizing the circuit design is just as beautiful as the sculpture.

At the focal point is the seven-segment LED display. Below it are four LEDs that show the current count's binary value. The LEDs in this sculpture are RGB, but Bhoite only made use of green. Driving these displays are two digital integrated circuits, a 74HC4060 and a 74HC47.

The 74HC4060 is a 14-stage ripple counter without the first four bits broken out into pins. This feature choice inherently makes the least significant bit of this chip a divide-by-16. Being a 14-bit counter means the maximum divide-by ratio is 16,384.

Four output bits, Q4-Q7, from the counter feed the inputs of the 74HC47. The '47 is doing the job it was made to do, driving a seven-segment LED display. After the sculpture displays the digit "9," it shows strange characters for a few more counts. These seemingly random patterns match up with counts 10 through 15, or, A through F in HEX.

This behavior might consume some people. It is not an error or a mistake. A quick look at a 74xx47's datasheet explains why. These chips are binary coded decimal (BCD) decoders. The emphasis there is decimal! As the datasheet explains, the patterns are not only expected but designed to output during those counts.

A helpful feature of the HC4060 counter chip is a built-in oscillator. Bhoite added a capacitor and two resistors to the oscillator pins to get the desired clock rate. We could not see the capacitor value in the pictures. However, based on the counting rate (about 1 per second) and knowing the '4060 is a divide-by-16, the target frequency is probably around 16 Hz. We can, however, clearly see the resistors on pins 10 and 11. Using a formula from the datasheet, we believe the capacitor is a 4.7 uF axial tantalum.

A 50 farad capacitor cell powers the entire circuit. While these usually get called "ultracapacitor" or "supercapacitor," both of those words are trade names. These cells are more correctly named "electrical-double layer capacitors" (ELDCs.) Speaking of capacitors, Bhoite even included a small decoupling capacitor for the ICs!

We cannot tell whether designing the circuit or building the freeform sculpture took more effort. Perhaps it was an equal amount! Regardless, the result is a beautiful and functional counter design. More pictures are available in this Twitter thread. You may also be interested in some of Bhoite's other sculptures. In the past, we have covered a few, such as the Compact LED VU Meter, Calculator and Clock, or the robot Chintoo.