Electronical design updates & future

I want to talk a little about the current development of the electronics board on my side since I would like some input from you guys.

The based the new design on the existing PSU and Arduino boards. The major changes are:

  1. Combined both boards into one
  2. Seperate Ground (Earth) and Power return paths
  3. Remove the common ground plane (EMI purposes), straight power path tracks
  4. Including a gas discharge tube footprint as lightning protection
  5. Set all stepper mode by solder jumpers (No change during operation, that causes loss of steps anyway)
  6. Changed dimension (67x110 mm)

I have tried to adapt the new design to follow these design rules:

  1. 26 mil width (for self manufacture)
  2. reduce vias (hand or cheap manufacture)
  3. Free Eagle limitations: 100x80 mm / 1 Sheet

The next improvements in developing I see are these:

  1. Include temperature sensore on the PCB by default
  2. Include input and opamp circuit for a position sensor potentiometer
  3. Increase the size to 160x100 mm to fit into a default euro size casing for EMI shielding, as these are most easy to get.

Hey! I have write some comments in your pull request. The next improvements is fine, because the V3 rotator is designed in order to mount dc or stepper motor (with change of the motor mount), we want to reduce the interference of motors and to have feedback from position of antennas.

For now we design the mechanical parts of V3 rotator (last 3 days) and we do not have a clear plan about the electronics.
We buy a dc motor like this DC motor, in order to test it with the V3 rotator. This is not the final choice, we will compare different types of motors (dc or stepper), with different characteristics in order to achieve our specs and a reasonable cost.
The V3 rotator is necessary to have position sensor, that measure every time the position of antennas. A good choice of it, is the AS5048 or AS5040 , which has different interfaces like I2C, SPI, PWM. The resolution of the sensor is 0.05deg or 0.35deg, but in the elevation axis we do not consider how to mount it. Also the price of the this sensor is not to high. An alternative method to measure the angles of two axis is planetsofa position sensor with pot. Has anyone try to use IMU? Do you have other ideas about it?

Additional sensors which checks the conditions inside and/or outside the rotator box is under consideration. The temperature sensor is a good idea, also a humidity sensor is useful, other sensors that you believe is necessary to add?

To reduce the interference of the motors and the electronics the EMI shielding and this look good ideas, other ideas about it?

Stay tuned for updates !!!

I have posted some response in the pull request.

Regarding AS5048: Neat part, I personally find it quite expensive :wink: But I think critical is rather this, both dc and stepper motors (even when off) have strong magnetic fields, even stronger when turned on. You can check this when your phone has a magnetometer (my Samsung S3 does) and the magnetic field values just go crazy, up to milliTesla. I think that can just mess up your magnetic measurements.

Is there anybody who has experience with magnetometers and acclerometers. I ordered an LSM303DLHC in order to experiment with automatic 0° positioning of the station. However, if it is precise enough (with magnetic deviation lookup table and propper calibration), it could be used as the sensor of the closed loop system for both axes when it’s mounted on the elevation axis. Although, if the magnetic field of the motors is already a big problem, a magnetometer might not be the best solution.

I have played with these devices. Its quite easy to achieve subdegree measurements with accelerometers for elevation I presume. However I wouldnt trust the magnetometer to much with the motors around. Your phone probably has a Magnetometer whose specs are very similar to these devices. You can play around with this android app ( https://play.google.com/store/apps/details?id=com.eclipsim.gpsstatus2&hl=de) to get the readings and get a feeling how feel these sensors perform.

I’m wondering if these effects you show can be corrected well enough with hard and soft iron magnetic compensation.
http://blog.memsindustrygroup.org/2011/03/22/hard-and-soft-iron-magnetic-compensation-explained/

With the motors being off, this shouldn’t be a problem. However, the changing unpredictable magnetic field of the running motors will probably affect the readings even more.

I shall give it a try as soon as I get my sensor and find some time.

Hey @planetsofa
Newbie here, gearing up to build this awesome project. In the middle of procuring the BOM, etc.
A few questions :

  1. A BBB alone could do this. Using the PRUs, we could probably get rid of the Arduino and knock off a few $. A cape which has the pololu drivers and the 12v regulator and that’s about it. Could nicely fit into a Altoids tin (everyone’s already using similar things to deal with the interference)
  2. Also, have you tried out KiCad for the PCB design ? It’s improved quite a bit recently.
1 Like

Hello @anuj

Yes its possible to do it of course, however it allows to seperate better into subsystems. The trackerbox has for instance arduino and router, the processing as client can be done somewhere else. That i think makes sense to keep processing outside (consider thermal). Otherwise, feel free to contribute a rotctrl to motor interface on Linux and its already done, but for said reasons its probably not for a default design.

KiCad was just favorably into discussion recently. If you feel proficent to convert feel free to contribute.

Generally, although sometimes i didnt understand some system design decision at first, but after understanding it often makes sense and is clever decision already by the SatNogs team:)

2 Likes

Since you are already adding a temp sensor, it might also be worth switching that to a combo temp+humidity sensor to guage if moisture is getting inside the enclosure. Combined with a desiccant pack, it would be easier to set a notification threshold based on internal moisture levels getting too high.

Also, since EMI reduction is important, and personally I’m putting my electronics inside an aluminum enclosure inside the V2 tracker box, you might also consider putting the temp+humidity sensor on a wire-lead which can live several inches away from the main board. At some future date when the tracker box enclosure is more stabilized it might be possible to do without the humidity sensor though. Just some food for thought.

Yes agreed we can implement an optional sensor at that position. Hardware-wise it can already be done with the existing hardware, since free 5V and IO are available on the Arduino breakout boards.

Software wise it would need to be implemented to read, but more particularly transfer the data via rotctld. With the updated EasyComm III I have implemented some features to read out options, such as temperature.

A good question would be: which sensor. I see a bunch of sensors with temp/hum which have a fairly simple interface.I guess DHT22 is an agreeable choice?

I’ve used the DHT22 and its relative the RHT03, they are good cheap dual temp+humidity sensors with easy Arduino library support and in an easy to use package. It uses a 1-wire style protocol but it’s not i2c so this does consume a single I/O line just for itself should that be a concern. Otherwise it’s a fine choice.

Hey,
we have started to design new electronics for DC motor version. We choose to design the PCBs in KiCAD, so we re-design the EndStop board and we want to do the same with other PCBs that are designed in eagle.

@planetsofa, in your repo you have a PCB with optical encoder, have you tested it?

1 Like

Didnt have the time yet… :frowning: