DSM501a IIR LPF - Infinite Response Low Pass filter

flow.js

[{"id":"fa93e49d.59c9d","type":"function","z":"44ba6b13.5c4d64","name":"IIR Low Pass Filter","func":"// IIR LPF factors\n  f_a0 = 0.0010227586546542474;     // Input factors\n  f_a1 = 0.002045517309308495;\n  f_a2 = 0.0010227586546542474;\n  \n  f_b1 = -1.9066459797557103;       // Output factors\n  f_b2 = 0.9107370143743273;\n\n// PPM 1.0 input variables\nvar i0_c10 = msg.payload.cPM10;\nvar i1_c10 = context.get('i1_c10') || 0;\nvar i2_c10 = context.get('i2_c10') || 0;\n\n// PPM 1.0 output variables\nvar o0_c10 = context.get('o0_c10') || 0;\nvar o1_c10 = context.get('o1_c10') || 0;\n\n\n// Calculate the IIR\nvar lpf =   i0_c10 * f_a0 + \n            i1_c10 * f_a1 + \n            i2_c10 * f_a2 -         // We add the negative output factors\n            o0_c10 * f_b1 - \n            o1_c10 * f_b2;\n            \n// Memorize the variables\ncontext.set( 'i2_c10' , i1_c10 );\ncontext.set( 'i1_c10' , i0_c10 );\n\ncontext.set( 'o1_c10' , o0_c10 );\ncontext.set( 'o0_c10' , lpf );\n\n// PPM 2.5 input variables\nvar i0_c25 = msg.payload.cPM25;\nvar i1_c25 = context.get('i1_c25') || 0;\nvar i2_c25 = context.get('i2_c25') || 0;\n\n// PPM 1.0 output variables\nvar o0_c25 = context.get('o0_c25') || 0;\nvar o1_c25 = context.get('o1_c25') || 0;\n\n\n// Calculate the IIR\nvar lpf25 =   i0_c25 * f_a0 + \n              i1_c25 * f_a1 + \n              i2_c25 * f_a2 -         // We add the negative output factors\n              o0_c25 * f_b1 - \n              o1_c25 * f_b2;\n            \n// Memorize the variables\ncontext.set( 'i2_c25' , i1_c25 );\ncontext.set( 'i1_c25' , i0_c25 );\n\ncontext.set( 'o1_c25' , o0_c25 );\ncontext.set( 'o0_c25' , lpf25 );\n\nmsg.payload = {}\nmsg.payload.cfP10 = lpf;\nmsg.payload.cfP25 = lpf25;\n\nreturn msg;","outputs":1,"noerr":0,"x":720,"y":40,"wires":[["273cea4a.08db0e","5d303ca9.50fdcc"]]}]