Rotary encoder for RPi + PI-DigiAmp+ with Moodeaudio

Support Raspberry Pi
21

Hi Victor

If you have a close look at the filter circuit you will see If you have the filter connected the 2 x 10kΩ resistors in series form the external pull up. Don’t use any other or you will have the same situation as using the internal resistor.
Cheers Bob

22

Yep thanks Bob, got it.
Cheers,
-Victor

23

Hi Victor

The bourns units do come with different shaft configurations.

image
image522×786 57.4 KB

If core don’t have what you are after Element 14 or RS Components should have the full range.
Postage is a bit prohibitive though to only buy 1 piece unless you can get to Chester Hill, NSW (Element 14) and pick up.
Cheers Bob

24

Hi Victor.
Just had a bit of a look at Element 14 rotary encoders. Mainly to get access to the data sheets.
I did note the Core encoder is the bourns PEC11 series and I am pretty sure the ones I have are the PEC11R series. I was interested to find out what the difference is.

The first thing I note is that Element 14 no longer stock the PEC11 series units.
The only other thing I can see (which is pretty important) is the PEC11 contacts are rated at 1mA while the PEC11R contacts are 10mA. The second thing is contact bounce is quoted 5mS for PEC11 and 2mS for PEC11R. A significant difference for both conditions.

I have been basing my experience (limited) on the PEC11R so if you are trying the PEC11 (no “R”) you may encounter some differences.

On the switch rating alone (1mA versus 10mA) I would suggest transferring allegiance to the PEC11R unit as 1mA is not giving you much fudge factor. If using that filter circuit and 3.3V supply you will be switch ig 0.33mA which is getting up to nearly half the maximum rating. You should get away with the PEC11 unit for trials, the only thing might be the bounce time but keep that in mind. It may cause the occasional error.

I also noted the data sheet for the PEC11 does not include that suggested filter circuit.
Cheers Bob

25

Thanks Bob. I think I am using PEC11R as this is the data sheet Core Electronics site is pointing to. Can’t see any marking on the unit itself.
Current ratings shouldn’t really matter as you noted. Contact bounce rating can of course make a difference, I get it. Having said that I am stuck with what I have at the moment anyway.
Definitely planning to try the ALPS unit in the future. Also thinking - in my case I have to use reasonably high powered switch mode PS (powering RPi + Amp bundle so need up to 3A capability as Core Electronics suggest). Wondering if the disturbances are coming form the PS.
As far as shaft length is concerned I am out of luck with standard units - need 65 mm. Encoder is going to be installed into the old radio case replacing normal volume pot so there are limitations :wink:
Cheers,
-Victor

26

Hi Victor

That link will take you to the PEC11 encoder. NOT the PEC11R.
That is why I looked it up, the data sheet I have saved on my PC is the PEC11R which is the data sheet I downloaded when I purchased mine, I bought 20 of them at the time. I am assuming that because the data sheet linked is for the PEC11 that is the one supplied. BUT you never know and probably won’t be able to find out.
And NO, I can’t find any markings either. Not even on the packets they came in, just antistatic sealed individual bags. And that was from Element 14.

If you use the 3.3V OUTPUT from the RPi that should be clean as it comes from the on board regulator on the Pi itself.

If you use a “standard” shaft with a flat there used to be readily available a double female coupler where you can attach this to your short shaft and fit an extension into the other end. Jaycar cat no YC2600.
Cheers Bob

27

Yes you are right, the data sheet is for PEC11, not PEC11R, I must have got confused it with one pointed to from the element 14 site.
Yes, using 3.3V from the RPi pin.
Unfortunately jaycar coupler won’t help as the shaft is passing through the plastic conduit of about 6.5mm internal diameter.
Thanks for your help.
Cheers,
-Victor

1 Like
28

Team, a quick update:
In addition to implementing hardware filter as suggested by Bob earlier, I have also made a slight modification to the python script / encoder driver (added bouncetime=5 parameter) and it seems to have completely solved my issue with occasional unreliable encoder operation:

Extract:

29

It seems the python code was omitted, here is the modification:

GPIO.add_event_detect(pin_a, GPIO.BOTH, callback=encoder_isr, bouncetime=5)
GPIO.add_event_detect(pin_b, GPIO.BOTH, callback=encoder_isr, bouncetime=5)

Cheers,
-Victor