{"id":664,"date":"2012-01-05T16:32:06","date_gmt":"2012-01-06T00:32:06","guid":{"rendered":"http:\/\/rustybolt.info\/wordpress\/?p=664"},"modified":"2012-03-14T18:55:20","modified_gmt":"2012-03-15T01:55:20","slug":"2012-01-05","status":"publish","type":"post","link":"https:\/\/rustybolt.info\/wordpress\/?p=664","title":{"rendered":"2012-01-05 Watson’s 3 LED Ring Oscillator"},"content":{"rendered":"

This simple circuit<\/a> acts somewhat like the LED Fader in that the LEDs do not turn on and off abruptly, however since the typical speed of the ring is faster than the fader, it’s harder to tell the turn-on and turn-off.\u00a0 It’s a fun circuit to build because of its simplicity and good visual effects.\u00a0 The circuit consists of three stages, each stage is identical to the others (see the schematic in the picture)\"\"<\/a>.<\/p>\n

Each stage is simple: an RC low pass filter, which is connected to the gate of a 2N7000 MOSFET.\u00a0 The LED and current limiting resistor are connected to the drain, and the source is connected to common negative.\u00a0 The low pass filter has the effect of shifting the phase of, or delaying the signal as it passes through, so the signal gets enough delay through the whole circuit to sustain oscillation.\u00a0 The values of the resistors and capacitors determine the speed of the LEDs turning on and off (for even speed, the values should be the same for all stages).<\/p>\n

Since the MOSFET does not need any current to the gate, the resistors can be any value up to megohms or millions of ohms.\u00a0 This allows us to use smaller capacitors, so the 0.1 uF plastic capacitors will work well with 1 meg resistors, as shown here.\u00a0 The 2N7000 requires about 2 volts to turn the gate on so the minimum supply voltage has to be the LED forward voltage (2 volts for red, 3V for blue) plus the gate voltage, or 5 to 6 volts.\u00a0 The supply voltage can be lowered somewhat by putting a resistor across each LED (I used 22k).<\/p>\n

The circuit will work with more stages, however the number of stages must be an odd number<\/strong><\/a>: 3, 5, 7, 9, etc.\u00a0 I built a 9 stage ring oscillator, but I later realized I could get a good enough effect by connecting every third LED in series and use only three stages.\u00a0 Of course the supply voltage has to be higher.<\/p>\n

I tried to build a similar circuit using regular BJTs (bipolar junction transistors), but I couldn’t get it to oscillate.\u00a0 I read that they require a pushbutton switch across one of the capacitors to short it out and get the oscillations to start, but I didn’t like that it had to have someone start it up.<\/p>\n

Thanks to Bill Sherman<\/a> for leading me to this circuit.\u00a0 I blogged this before, I’ll have to see if I can find that blog.<\/p>\n

Back to experimenting…<\/p>\n","protected":false},"excerpt":{"rendered":"

This simple circuit acts somewhat like the LED Fader in that the LEDs do not turn on and off abruptly, however since the typical speed of the ring is faster than the fader, it’s harder to tell the turn-on and turn-off.\u00a0 It’s a fun circuit to build because of its simplicity and good visual effects.\u00a0 <\/p>\n

(Read More…)<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-664","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/664","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=664"}],"version-history":[{"count":15,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/664\/revisions"}],"predecessor-version":[{"id":1555,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/664\/revisions\/1555"}],"wp:attachment":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=664"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=664"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=664"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}