I went way down the rabbit hole trying to convert RSSI (in dBm) to a useful signal strength meter, like you’d see on your cell phone.<\/p>\n
I read many articles, but no one really had an algorithm.\u00a0 So….here is an algorithm written in Javascript.<\/p>\n
<\/p>\n
\/\/This assumes you have a way to obtain rssi... in my application,\r\n\/\/ this is the rssi for the web server's connection (IoT device).\r\n\r\nfunction rssiToBars( rssi , maxbars ){\r\n var ret=rssi+80; \/\/Useful range is -80 (bad) to -30 (good).\r\n \/\/+50 converts this to a useful range of 0 (bad) to 50 (good)\r\n\r\n ret=(ret< 0)?0:rssi; \/\/Clamping\r\n ret=(ret>50)?50:rssi;\r\n\r\n ret=parseInt(ret*maxbars\/50); \/\/taking a percent (rssi\/50) of maxbars\r\n\r\n \/\/ If you are using a language with integer data types, make sure you multiply\r\n \/\/ first, then divide.\r\n\r\n return(ret);\r\n}\r\n\r\nfunction rssiMeter( bars , maxbars ){\r\n return(\"<PRE>[\" + \"#\".reapeat(bars) + \"-\".repeat(maxbars-bars) + \"]<\/PRE>\");\r\n\r\n \/\/This is a simple example, but you could stack a couple of small PNG or \r\n \/\/render a table where the cells are bars.\r\n}\r\n\r\nconst maxbars=8\r\nvar rssi=-55; \/\/some magical way to get the rssi\r\nvar bars=rssiToBars(rssi,maxbars);\r\nvar meter=rssiMeter( bars , maxbars);\r\n\r\n\/\/ rssi == -55\r\n\/\/ bars == 4\r\n\/\/ meter == <PRE>[####---]<\/PRE>\r\n\r\n<\/pre>\n <\/p>\n
How It Works<\/h2>\n
Received Signal Strength Indicator (RSSI) is the relative signal strength of a transmitter, from the receiver’s perspective.<\/p>\n
RSSI is measured in dBm, or Decibel-milliWatts.\u00a0 Basically, this is milliWatts as perceived by the receiver, but represented on a logarithmic scale.<\/p>\n
Because power drops inversely with the square of the distance, a logarithmic scale more or less represents this as a linear scale, rather than exponential.<\/p>\n
For example, if you have signal strength of -30 (very good) and you walk 50 feet away with no obstacles between you and the router, you might drop to -40 dBm.\u00a0 If you walk another 50 feet, you would expect the signal to drop to -50 dBm.\u00a0 This a super-simple example, and there are a lot of other factors involved, but you get the basic idea.<\/p>\n
The algorithm works like this:<\/p>\n
\n- Convert rssi to a useful scale.\u00a0 We do this by adding 80.\u00a0 If we start with a range of -30 (good) to -80 (bad) and add 30, we get 0 (good) to -50 (bad).\u00a0 Further if we add 50, we get a positive integer that is now reversed:\u00a0 -50+50==0 (bad) and 0+50==50 (good).<\/li>\n
- Next, we clamp the values to prevent unexpected results, ensuring we now have an integer in the range of 0..50.<\/li>\n
- Dividing this number by 50 yields a percentage (0..1)<\/li>\n
- Multiplying the percentage by the max number of bars, gives you the number of bars.\u00a0 For example, .5 * 8\u00a0 (medium signal strength * 8 bars) == 4.<\/li>\n
- If using a typed language such as c++, be sure to multiply first, THEN divide:\u00a0 (rssi+50)*maxbars\/50.\u00a0 If not, the CPU will perform int math, and bars will be zero most of the time.<\/li>\n<\/ol>\n
Rendering can be done however you want.\u00a0 One slick trick is to use CSS and a small table, where each cell is a bar, and CSS dictates the cell color.\u00a0 Your code sets the class of each cell to “bar” or “nobar”.<\/p>\n
<STYLE>\r\n.bar , .nobar {\r\n height: 10px;\r\n width: 10px;\r\n border: 1px solid gray;\r\n border-collapse:collaps;\r\n font-size: 1px;\r\n}\r\n\r\n.bar{\r\n background-color: #0000FF \/\/Blue\r\n}\r\n\r\n.nobar{\r\n background-color: #000022 \/\/Dark Blue\r\n}\r\n<\/STYLE>\r\n<SCRIPT>\r\n function rssiMeter( bars , maxbars ){\r\n var meter=\"<TABLE STYLE='border-collapse:collapse;'><TR>\";\r\n\r\n for(var i=0 ; i<maxbars ; i++){\r\n var class=(i<bars)?\"bar\":\"nobar\";\r\n meter+=\"<TD CLASS=\"+class+\"> \"; \r\n \/\/NO I DO NOT CLOSE MY TD TAGS. SUE ME\r\n }\r\n\r\n meter+=\"<\/TR><\/TABLE>\";\r\n\r\n return(meter);\r\n }\r\n\r\n \/\/ you can attach it to a DIV like this:\r\n const maxbars=8; \/\/ define constants at the top of your script\r\n const divname=\"meter\"; \r\n\r\n function updateMeter(){\r\n var rssi = somenumber; \r\n var bars = rssiToBars(rssi , maxbars); \/\/maxbars is a global const\r\n var meter= rssiMeter( bars , maxbars); \r\n document.getElementById(divname).innerHTML=meter; \/\/divname is a global const\r\n }\r\n\r\n \/\/ be sure there is <DIV ID=meter> <\/DIV>\r\n \/\/ somewhere in your document\r\n\r\n \/\/Now, whenever you want to update your meter:\r\n updateMeter();\r\n\r\n<\/SCRIPT><\/pre>\nEnjoy!<\/p>\n","protected":false},"excerpt":{"rendered":"
Convert WiFi RSSI to Signal Bars (Formula and Code Snippet) I went way down the rabbit hole trying to convert RSSI (in dBm) to a useful signal strength meter, like you’d see on your cell phone. I read many articles, but no one really had an algorithm.\u00a0 So….here is an algorithm written in Javascript. […]<\/p>\n","protected":false},"author":16,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"aside","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-7928","post","type-post","status-publish","format-aside","hentry","category-other-stuff","post_format-post-format-aside"],"_links":{"self":[{"href":"https:\/\/justinparrtech.com\/JustinParr-Tech\/wp-json\/wp\/v2\/posts\/7928","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/justinparrtech.com\/JustinParr-Tech\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/justinparrtech.com\/JustinParr-Tech\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/justinparrtech.com\/JustinParr-Tech\/wp-json\/wp\/v2\/users\/16"}],"replies":[{"embeddable":true,"href":"https:\/\/justinparrtech.com\/JustinParr-Tech\/wp-json\/wp\/v2\/comments?post=7928"}],"version-history":[{"count":8,"href":"https:\/\/justinparrtech.com\/JustinParr-Tech\/wp-json\/wp\/v2\/posts\/7928\/revisions"}],"predecessor-version":[{"id":7936,"href":"https:\/\/justinparrtech.com\/JustinParr-Tech\/wp-json\/wp\/v2\/posts\/7928\/revisions\/7936"}],"wp:attachment":[{"href":"https:\/\/justinparrtech.com\/JustinParr-Tech\/wp-json\/wp\/v2\/media?parent=7928"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/justinparrtech.com\/JustinParr-Tech\/wp-json\/wp\/v2\/categories?post=7928"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/justinparrtech.com\/JustinParr-Tech\/wp-json\/wp\/v2\/tags?post=7928"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}