Step counter activity (#1216)

* added step-counter project

* added to summary

docs/projects/step-counter.md

@@ -0,0 +1,67 @@
+# Step counter
+
+![A @boardname@ attached on a foot](/static/mb/projects/step-counter.png)
+
+This project turns the @boardname@ into a simple step-counter.
+Each **shake** event increment a **counter** variable.
+
+## ~ hint
+
+If you built a watch in the [make](/projects/watch/make) portion of the of the [Watch](/projects/watch) project, you can use the code from this project with it too.
+
+## ~
+
+## A counter
+
+To build a counter, we will need a variable to store the number of steps.
+
+```blocks
+let step = 0
+step = 0
+```
+
+## Detecting a step
+
+Assuming you attach the @boardname@ to your foot, it will get shaken up when do a step. We can use the ``||input:on shake||`` event to detect a step (it should work most of the time). Let's add the code to increment ``step`` by 1 when @boardname@ is shaken.
+
+```blocks
+let step = 0
+input.onGesture(Gesture.Shake, function () {
+    step += 1
+})
+step = 0
+```
+
+## How many steps so far?
+
+We want to see the number of steps at all time. In a ``||basic:forever||`` loop,
+we add a ``||basic:show number||`` block to display the value of ``step``.
+
+```blocks
+let step = 0
+input.onGesture(Gesture.Shake, function () {
+    step += 1
+})
+basic.forever(function() {
+    basic.showNumber(step)
+})
+step = 0
+```
+
+## Display lag
+
+Did you notice there is a lag in the display of steps? 
+This is because the ``step`` value can change **while** the @boardname@ is displaying a number.
+To remove the lag, add ``||led:stop animation||`` after changing the value of ``step``.
+
+```blocks
+let step = 0
+input.onGesture(Gesture.Shake, function () {
+    step += 1
+    led.stopAnimation()
+})
+basic.forever(function() {
+    basic.showNumber(step)
+})
+step = 0
+```