On Sat, 14 Mar 2020, Andrew wrote:
Date: Sat, 14 Mar 2020 18:24:25 +0200
From: Andrew <[email protected]>
Reply-To: "Enhanced Machine Controller (EMC)"
<[email protected]>
To: "Enhanced Machine Controller (EMC)" <[email protected]>
Subject: [Emc-users] Mesa boards for RPi 4
Hello!
I need to control a small machine with 3 Copley Controls Junus drives and
5V incremental encoders on the motors.
I would like to keep the cost as low as possible. Luckily Junus has PWM
inputs and I don't need analog outputs.
I am going to buy RPi 4 for this project.
1. Anyone has experience with RPi 4 and 7i90HD via SPI link? When I tried
it with RPi 3, the link was really unstable.
The RPI 4 will not be any different in this respect
SPI signal integrity goes down exponentially with cable length
and ground impedance must be low, so I would not expect decent
reliability with cables any longer than about 3 inches and
using all 8 ground connections on the RPI
2. Assuming the first reply negative and I use 7i92: do I have to buy 7i85
or 7i75 is enough protection for FPGA chip? Or is it possible to connect
encoder outputs and PWM inputs (74HC14) directly to 7i92?
You can connect encoder and PWM pins direct to the FPGA card but beware of
noise sources like servo drives that can cause multi-volt HF ground bumping.
FPGA/Bus Switch pins need to be protected from unlimited current negative spikes
(a 100 ohm or so series resistor provides some protection)
3. Any other option?
Thanks and best regards,
Andrew
_______________________________________________
Emc-users mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/emc-users
Peter Wallace
Mesa Electronics
(\__/)
(='.'=) This is Bunny. Copy and paste bunny into your
(")_(") signature to help him gain world domination.
_______________________________________________
Emc-users mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/emc-users
