{"id":9781,"date":"2024-03-25T11:53:26","date_gmt":"2024-03-25T11:53:26","guid":{"rendered":"https:\/\/www.bairesdev.com\/tools\/tessel\/?p=9781"},"modified":"2024-05-09T11:05:53","modified_gmt":"2024-05-09T11:05:53","slug":"pulse-width-modulation-pwm","status":"publish","type":"post","link":"https:\/\/www.bairesdev.com\/tools\/tessel\/docs\/pulse-width-modulation-pwm\/","title":{"rendered":"Pulse-width Modulation (PWM)"},"content":{"rendered":"\n

PWM pins<\/strong> are pulse-width modulated pins. Essentially, PWM is a digital signal that spends between 0% and 100% of its time pulled high\/on (this is its “duty cycle”). You can set the PWM pins to any value between 0 (0%) and 1 (100%) to approximate an analog signal. PWM is often used to control servo speeds or LED brightness.<\/p>\n\n\n\n

In the following example, the Tessel will change the color of an RGB LED by changing the duty cycle sent to each color pin over a set interval of time. By changing the brightness of each internal LED (red, green, blue) per cycle, the combined color of the RGB component is changed.<\/p>\n\n\n\n

<\/circle><\/circle><\/circle><\/g><\/svg><\/span><\/path><\/path><\/svg><\/span>
var<\/span> <\/span>tessel<\/span> <\/span>=<\/span> <\/span>require<\/span>(<\/span>'<\/span>tessel<\/span>'<\/span>)<\/span>;<\/span> <\/span>\/\/ Import tessel<\/span><\/span>\n<\/span>\nvar<\/span> <\/span>portA<\/span> <\/span>=<\/span> <\/span>tessel<\/span>.<\/span>port<\/span>.<\/span>A<\/span>;<\/span> <\/span>\/\/ Select port A<\/span><\/span>\nvar<\/span> <\/span>portB<\/span> <\/span>=<\/span> <\/span>tessel<\/span>.<\/span>port<\/span>.<\/span>B<\/span>;<\/span> <\/span>\/\/ Select port B<\/span><\/span>\n<\/span>\nvar<\/span> <\/span>redPin<\/span> <\/span>=<\/span> <\/span>portA<\/span>.<\/span>pwm<\/span>[<\/span>0<\/span>]<\/span>;<\/span> <\/span>\/\/ Select the first PWM pin on port A, equivalent to portA.pin[5]<\/span><\/span>\nvar<\/span> <\/span>greenPin<\/span> <\/span>=<\/span> <\/span>portA<\/span>.<\/span>pwm<\/span>[<\/span>1<\/span>]<\/span>;<\/span><\/span>\nvar<\/span> <\/span>bluePin<\/span> <\/span>=<\/span> <\/span>portB<\/span>.<\/span>pwm<\/span>[<\/span>0<\/span>]<\/span>;<\/span><\/span>\n<\/span>\n\/\/ The starting values of each color out of 255<\/span><\/span>\nvar<\/span> <\/span>red<\/span> <\/span>=<\/span> <\/span>0<\/span>;<\/span><\/span>\nvar<\/span> <\/span>green<\/span> <\/span>=<\/span> <\/span>0<\/span>;<\/span><\/span>\nvar<\/span> <\/span>blue<\/span> <\/span>=<\/span> <\/span>0<\/span>;<\/span><\/span>\n<\/span>\n\/\/ Use this to increment the color value without exceeding 255<\/span><\/span>\nfunction<\/span> <\/span>stepColor<\/span> <\/span>(<\/span>value<\/span>,<\/span> <\/span>step<\/span>)<\/span> <\/span>{<\/span><\/span>\n  <\/span>value<\/span> <\/span>+=<\/span> <\/span>step<\/span>;<\/span> <\/span>\/\/ Add the step count to the existing value<\/span><\/span>\n<\/span>\n  <\/span>\/\/ If the value exceeds 255, then reset it to 0<\/span><\/span>\n  <\/span>if<\/span> (<\/span>value<\/span> <\/span>><\/span> <\/span>255<\/span>) <\/span>{<\/span><\/span>\n    <\/span>value<\/span> <\/span>=<\/span> <\/span>0<\/span>;<\/span><\/span>\n  <\/span>}<\/span><\/span>\n<\/span>\n  <\/span>return<\/span> <\/span>value<\/span>;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\n\/\/ Set the signal frequency to 1000 Hz, or 1000 cycles per second<\/span><\/span>\n\/\/ This the rate at which Tessel will send the PWM signals<\/span><\/span>\n\/\/ This is program specific<\/span><\/span>\ntessel<\/span>.<\/span>pwmFrequency<\/span>(<\/span>1000<\/span>)<\/span>;<\/span><\/span>\n<\/span>\n\/\/ Create a loop to run a function at a set interval of time<\/span><\/span>\nsetinterval<\/span>(<\/span>function<\/span>()<\/span> <\/span>{<\/span><\/span>\n  <\/span>\/\/ Increment each color at a unique step<\/span><\/span>\n  <\/span>red<\/span> <\/span>=<\/span> <\/span>stepColor<\/span>(<\/span>red<\/span>,<\/span> <\/span>10<\/span>)<\/span>;<\/span><\/span>\n  <\/span>bluE<\/span> <\/span>=<\/span> <\/span>stepColor<\/span>(<\/span>blue<\/span>,<\/span> <\/span>5<\/span>)<\/span>;<\/span><\/span>\n  <\/span>green<\/span> <\/span>=<\/span> <\/span>stepColor<\/span>(<\/span>green<\/span>,<\/span> <\/span>20<\/span>)<\/span>;<\/span><\/span>\n<\/span>\n  <\/span>\/\/ Set how often each pin is turned on out of 100%<\/span><\/span>\n  <\/span>\/\/ Divide the value by 255 to get a value between 0 and 1<\/span><\/span>\n  <\/span>redPin<\/span>.<\/span>pwmDutyCycle<\/span>(<\/span>red<\/span> <\/span>\/<\/span> <\/span>255<\/span>)<\/span>;<\/span><\/span>\n  <\/span>greenPin<\/span>.<\/span>pwmDutyCycle<\/span>(<\/span>blue<\/span> <\/span>\/<\/span> <\/span>255<\/span>)<\/span>;<\/span><\/span>\n  <\/span>bluePin<\/span>.<\/span>pwmDutyCycle<\/span>(<\/span>green<\/span> <\/span>\/<\/span> <\/span>255<\/span>)<\/span>;<\/span><\/span>\n},<\/span> <\/span>500<\/span>)<\/span>;<\/span> <\/span>\/\/ Set this function to be called every 500 milliseconds, or every half a second<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
Note: the pwmFrequency<\/code> function must<\/em> be called before pwmDutyCycle<\/code>. Re-setting pwmFrequency<\/code> will disable PWM output until pwmDutyCycle<\/code> is called again.<\/p>\n","protected":false},"excerpt":{"rendered":"
PWM pins are pulse-width modulated pins. Essentially, PWM is a digital signal that spends between 0% and 100% of its time pulled high\/on (this is its “duty cycle”). You can set the PWM pins to any value between 0 (0%) and 1 (100%) to approximate an analog signal. PWM is often used to control servo speeds or LED brightness. In the following example, the Tessel will change the color of an […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4,59],"tags":[],"class_list":["post-9781","post","type-post","status-publish","format-standard","hentry","category-docs","category-tutorials"],"_links":{"self":[{"href":"https:\/\/www.bairesdev.com\/tools\/tessel\/wp-json\/wp\/v2\/posts\/9781","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.bairesdev.com\/tools\/tessel\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.bairesdev.com\/tools\/tessel\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.bairesdev.com\/tools\/tessel\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.bairesdev.com\/tools\/tessel\/wp-json\/wp\/v2\/comments?post=9781"}],"version-history":[{"count":3,"href":"https:\/\/www.bairesdev.com\/tools\/tessel\/wp-json\/wp\/v2\/posts\/9781\/revisions"}],"predecessor-version":[{"id":10077,"href":"https:\/\/www.bairesdev.com\/tools\/tessel\/wp-json\/wp\/v2\/posts\/9781\/revisions\/10077"}],"wp:attachment":[{"href":"https:\/\/www.bairesdev.com\/tools\/tessel\/wp-json\/wp\/v2\/media?parent=9781"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bairesdev.com\/tools\/tessel\/wp-json\/wp\/v2\/categories?post=9781"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bairesdev.com\/tools\/tessel\/wp-json\/wp\/v2\/tags?post=9781"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}