diff --git a/pf.js b/pf.js
index 85b35bf..d25332c 100644
--- a/pf.js
+++ b/pf.js
@@ -1,7 +1,12 @@
 const random = require('random')
 const dayjs = require('dayjs')
+let debug = (msg) => null
 
-function createSchedule ({
+function setDebugFn(debugFn) {
+  debug = debugFn
+}
+
+function createSchedule({
   windowBegin,
   windowEnd,
   minDuration,
@@ -35,7 +40,7 @@ function createSchedule ({
 
   const calcRandomNumber = (min, max) => random.int(min, max)
 
-  const sumDurations = blocks =>
+  const sumDurations = (blocks) =>
     blocks.reduce((prev, curr) => prev + curr.duration, 0)
 
   const randomCount = calcRandomCount()
@@ -50,13 +55,13 @@ function createSchedule ({
     })
   }
 
-  // remove as many blocks as needed to fit the time window
+  // remove as many on-blocks as needed to fit the time window
   while (sumDurations(onBlocks) >= windowDuration) {
     onBlocks.shift()
   }
 
   // add one block if none was left:
-  if (onBlocks.length == 0) {
+  if (randomCount > 0 && onBlocks.length == 0) {
     onBlocks.push({
       isOn: true,
       duration: Math.floor(windowDuration * 0.9), // spans 90% of the window
@@ -82,7 +87,7 @@ function createSchedule ({
 
   const sumOfRandom = offBlocks.reduce((acc, curr) => acc + curr.random, 0)
 
-  offBlocks.map(block => {
+  offBlocks.map((block) => {
     const factor = block.random / sumOfRandom
     block.duration = Math.floor(sumOffDurations * factor)
     delete block.random
@@ -101,7 +106,7 @@ function createSchedule ({
   return _calcScheduleTimes(schedule, windowBegin)
 }
 
-function _combineBlocks (offBlocks, onBlocks, firstBlockType) {
+function _combineBlocks(offBlocks, onBlocks, firstBlockType) {
   let schedule = []
 
   const greenBlocks = firstBlockType === 'off' ? offBlocks : onBlocks
@@ -122,8 +127,8 @@ function _combineBlocks (offBlocks, onBlocks, firstBlockType) {
   return schedule
 }
 
-function _calcScheduleTimes (schedule, start) {
-  schedule.forEach(block => {
+function _calcScheduleTimes(schedule, start) {
+  schedule.forEach((block) => {
     block.beginString = start.format('HH:mm:ss')
     let end = start.add(block.duration, 'second')
     block.endString = end.format('HH:mm:ss')
@@ -134,12 +139,12 @@ function _calcScheduleTimes (schedule, start) {
   return schedule
 }
 
-function stripPastBlocks (blocks) {
+function stripPastBlocks(blocks) {
   const now = dayjs()
-  return blocks.filter(block => {
+  return blocks.filter((block) => {
     let end = block.begin.add(block.duration, 'second')
     return now.isBefore(end)
   })
 }
 
-module.exports = { createSchedule, stripPastBlocks }
+module.exports = { createSchedule, stripPastBlocks, setDebugFn }
diff --git a/presence-faker.js b/presence-faker.js
index fdf2a7c..6edfb92 100644
--- a/presence-faker.js
+++ b/presence-faker.js
@@ -1,9 +1,9 @@
-const { createSchedule, stripPastBlocks } = require('./pf')
+const { createSchedule, stripPastBlocks, setDebugFn } = require('./pf')
 const CronJob = require('cron').CronJob
 const dayjs = require('dayjs')
 
 module.exports = function (RED) {
-  function PresenceFakerNode (config) {
+  function PresenceFakerNode(config) {
     RED.nodes.createNode(this, config)
 
     const node = this
@@ -18,6 +18,8 @@ module.exports = function (RED) {
       }
     }
 
+    setDebugFn(debug)
+
     const setNodeStatusForBlock = function (block) {
       const text = `${block.isOn ? 'ON' : 'OFF'} [${block.beginString} - ${
         block.endString
@@ -112,7 +114,7 @@ module.exports = function (RED) {
     }
 
     const scheduleMsgCrons = function (schedule) {
-      msgCrons = schedule.map(block => {
+      msgCrons = schedule.map((block) => {
         const cron = new CronJob({
           cronTime: block.begin.toDate(),
           onTick: () => {
@@ -142,7 +144,7 @@ module.exports = function (RED) {
       let deletedCronsCount = 0
 
       if (msgCrons.length > 0) {
-        msgCrons.forEach(cron => {
+        msgCrons.forEach((cron) => {
           cron.stop()
           deletedCronsCount++
         })
@@ -153,7 +155,7 @@ module.exports = function (RED) {
       debug(`${deletedCronsCount} message crons deleted`)
     }
 
-    const executeBlock = block => {
+    const executeBlock = (block) => {
       debug('executing block: ' + JSON.stringify(block))
       ejectMsg(block.isOn)
       setNodeStatusForBlock(block)