Numitron Clock with Battery Back-up

The idea was that you removed the center page from the magazine and cut it into four pieces to obtain a card that would fit into a filing system. The front side of each card would gave the connections to the IC, while the other side would contain technical details and an application circuit.
Numitron Clock with Battery Back-up - schematic

Fig. 1 depicts, as an example, the front- and back-side of the IC-card for the 74141 nixie driver. Intrigued as I was by the mysterious symbols, these cards enabled me to decipher the basic ideas behind digital electronics. And like most things in life, once you have mastered the basics, the rest comes pretty smoothly. For years I was obsessed by the possibilities of these small black building blocks. It soon became my dream to build a digital counter with display. Now you have to remember that in those days something like a seven segment display was something that not that many people, including myself, had seen in real life. So for my birthday I asked a SN7490 decade counter, a SN7447 BCD to seven-segment decoder, and a 3015-F Numitron display. In those days these components were rather expensive! In the same Elektuur magazine from which the Fig. 1 IC-card was taken, I have an advertisement which offered these components. In the table below, you will find the prices of these components as they were then in guilders, but also in the price in Euro now, based on the ratio of the prices of the Elektuur magazine then (fl 1. 95) and now (Euro 6. 85). Even if I am mistaken by a factor of two, than still it was a lot of money. I still remember my mother saying that she had never paid so much money for so little. My grandmother on seeing the goods and hearing the price was, I believe, in shock for days. I still have the Minitron...

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