This was around 1972 when I lived in Flanders, NJ with my parents, younger brother Bill, and older brother Jim.<\/p>\n\n\n\n
Bill had an 8-track player, but it didn\u2019t have any indicators as to which of the 4 stereo tracks was playing. All it had was a square white button that would change to the next track. I offered to open it up and look at the mechanism to see if it would be feasible to add a display. At the time I was thinking about maybe 4 LEDs or something.<\/p>\n\n\n\n
Much to my amazement, there was an unconnected terminal strip with four dry contacts to a common. I also found a positive power supply. It looked to me that the mechanism was the same as would be used in a \u201chigher-end\u201d player with indicators. The only problem was that there wasn\u2019t room on the front bezel for 4 indicators. But there was just enough room for a single 0.3″ 7-segment LED display.<\/p>\n\n\n\n
At around age 14, this was my first try at an electronics design. Up until then, all my electronics experience came from a Radio Shack 100-in-one experimenter\u2019s kit. These things were a collection of components line an antenna, germanium diodes and transistors, relay, resistors, and capacitors. It came with circuits to build an AM radio, a photo-cell detector, audio amplifier, etc. By the time I got done with it, I had destroyed both transistors and figured out how to wire the relay to self-oscillate with a 9-volt battery and send the signal to the secondary of the audio transformer. Yeah, you could definitely feel the voltage on the primary side!<\/p>\n\n\n\n
Needless to say, I had no idea what Ohm\u2019s law was. But that wasn\u2019t going to stop me, because I didn\u2019t know what I didn\u2019t know\u2026 But, how hard could it be? It\u2019s just a bit of logic to convert one-of-four to 7-segment. I knew about diodes (or at least the first-order approximation of them), and that the display LEDs lit up when you applied voltage (note that I didn\u2019t say current). So I drew up a diode logic diagram that would display the digits 1, 2, 3, and 4 based on which of the transport contacts were closed. I confidently ordered a display and a SIP diode array from Poly Paks and got to work wiring it up. It worked for a brief moment before the magic smoke was released. What could have gone wrong?<\/p>\n\n\n\n
My friend Bruce McIntyre from high school to the rescue. He knew things like Ohm\u2019s law. He explained things like forward voltage drop and current needed for an LED segment. So, I need resistors, then? You mean I will need to use my calculator? So I added series resistors to the original diode logic diagram and son-of-a-gun it worked! I drilled a large hole in the bezel and epoxied the display and diode SIP in place. It worked until Bill got rid of the player many years later.<\/p>\n\n\n\n
So, at this point I\u2019m comfortable with diode logic and current-limiting resistors. Just don’t ask me how a transistor works\u2026<\/p>\n","protected":false},"excerpt":{"rendered":"
This was around 1972 when I lived in Flanders, NJ with my parents, younger brother Bill, and older brother Jim. Bill had an 8-track player, but it didn\u2019t have any indicators as to which of the 4 stereo tracks was playing. All it had was a square white button that would change to the next […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":130,"menu_order":1972,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"jetpack_sharing_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/robertweatherford.com\/index.php\/wp-json\/wp\/v2\/pages\/158"}],"collection":[{"href":"https:\/\/robertweatherford.com\/index.php\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/robertweatherford.com\/index.php\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/robertweatherford.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/robertweatherford.com\/index.php\/wp-json\/wp\/v2\/comments?post=158"}],"version-history":[{"count":3,"href":"https:\/\/robertweatherford.com\/index.php\/wp-json\/wp\/v2\/pages\/158\/revisions"}],"predecessor-version":[{"id":641,"href":"https:\/\/robertweatherford.com\/index.php\/wp-json\/wp\/v2\/pages\/158\/revisions\/641"}],"up":[{"embeddable":true,"href":"https:\/\/robertweatherford.com\/index.php\/wp-json\/wp\/v2\/pages\/130"}],"wp:attachment":[{"href":"https:\/\/robertweatherford.com\/index.php\/wp-json\/wp\/v2\/media?parent=158"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}