forum.hobbycomponents.com

Hi,

First of all, I am posting this here as there is no "New Topic" button in the Modules board where it ought to go.

My question is - has anyone bought the IR Infrared Speed Sensing Module from Hobby Components? It is supposed to be "ideal" for the 4WD smart car they sell but I can't work out how it is supposed to fit. Having bodged a fit and tested it, I was getting very erratic readings from an Arduino that was counting the pulses using the D2/D3 hardware pin interrupt. The Arduino counted pulses from another Arduino just fine so the sketch is working OK. When I looked at the waveform being put out by the sensor on an oscilloscope it had about a 90% duty cycle and loads of ripple, so hardly surprising the arduino was struggling to read it.

I put the signal through a schmitt trigger and that cured the positive wave ripple but not the "off" ripple or the erratic readings from the Arduino. I bought a different sensor off ebay and that fit the chassis even worse than the Hobby Components one but I was able to wedge it on for testing. Signal output with the motors running and the same wiring as the Hobby Components module gave a perfectly smooth waveform with a pretty much 50% waveform. I also noticed that when just putting a piece of card in the slot manually , unless the card was right against one side of the sensor the oscilloscope pattern had some very weird reflection type noise - not present with the other sensor.

I am wondering whether I am missing something obvious or whether these Hobby Components sensors are simply not fit for purpose. How HC can claim they are "ideal" for their 4WD smart car chassis when they neither fit or give reliable readings is beyond me.

So I suppose I have two specific questions;
1. Has anyone got the Hobby Components sensor working with the 4WD smart car chassis (if so , how)
2. Is there a sensor out there that will fit the chassis and read the slotted wheel encoder discs reliably.

Many thanks

First of all, I am posting this here as there is no "New Topic" button in the Modules board where it ought to go.

We don't allow new topics to be created in products area to try and keep it organised. Sorry about there being no topic for the speed sensing module, this is an oversight and we will get this added as soon as possible. The general topics area is intended for creating your own topic threads.

It is supposed to be "ideal" for the 4WD smart car they sell but I can't work out how it is supposed to fit.

There are some '+' shaped slots cut into the chassis directly above each of the 4 encoder discs. The module fits into these slots and sit either side of encoder wheel. Unfortunately for some reason the manufacturer of the car decided not to pre-drilled the chassis for mounting holes (maybe to be compatible with different types of modules) so you will need to drill these in the appropriate place.

When I looked at the waveform being put out by the sensor on an oscilloscope it had about a 90% duty cycle and loads of ripple, so hardly surprising the arduino was struggling to read it.

The duty cycle is mainly governed by the slot sizes on the encoder disc. As the slots are much wider then the spaces in between them, you won't see a 50% duty cycle. That said, I would expect you to be seeing something more like a 75% duty, not 90%. You should also not be seeing a 'ripple'. This could be caused by all sorts of things such as wires that are too long, poor grounding, or an un-smoothed power supply. Did you put your scope across the power supply at the module (especially when the motors are running) to see if this ripple is present on the supply? What are you using as a power supply? Can you measure the frequency of the ripple?

also noticed that when just putting a piece of card in the slot manually , unless the card was right against one side of the sensor the oscilloscope pattern had some very weird reflection type noise

Could you elaborate on what you mean by reflection noise? Maybe a grab of your oscilloscope screen?