Programming the Raspberry Pi

[wimvb]

On ‎2016‎-‎08‎-‎12 at 21:44, Gina said:

Been doing some reading and it seems the RPi 3 needs up to 2.5A and not standard USB 500mA - maybe I got a cable for an early RPi model.  Anyway, for while I'm experimenting, I've ordered a genuine RPi power supply.  Also, reading the RPi web site it seems the RPi 3 wants 5.1v rather than 5v.  For astronomy use I shall make up a special power cable and run the RPi from a "buck converter" or other voltage regulator, from my 13.8v observatory power supply.

AFAIK the RPi has a micro usb connector that is used for power only. This needs to be connected to a power supply that can provide a higher current than the standard 500 mA that comes from a computers usb. I.e. while the connector is usb, only the power lines within it are used. Very much like a charger for a mobile phone.

You could try a 12 V car plug that has a built in usb connector, with a standard usb - micro usb cable

[Gina]

I took the USB plug off the cable and connected it to 5v from a bench PSU and that's fine

[kens]

1 hour ago, wimvb said:

Do you control this stuff with the RPi (running a server like indi)? Or do you channel the equipment through the RPi to your computer (virtual usb ports)?

I'm running Indi on the RPi and connecting to my desktop with Wifi where I run Ekos. I've only done a few trials but it seems to be ok. I'm also going to try connecting to the mount with Bluetooth from the RPi. I haven't yet made the jump as I'm working through some other power/wiring issues and don't want to muddy the waters with too many new components.

[wimvb]

2 hours ago, kens said:

I'm running Indi on the RPi and connecting to my desktop with Wifi where I run Ekos. I've only done a few trials but it seems to be ok. I'm also going to try connecting to the mount with Bluetooth from the RPi. I haven't yet made the jump as I'm working through some other power/wiring issues and don't want to muddy the waters with too many new components.

Does that mean that you use the RPi for guiding as well? I would be interested in knowing your setup. I've been thinking about using the RPi with Linguider. That is one of the reasons I have been testing the camera. Maybe the camera with RPi and linguider would make a nice standalone budget guiding unit.

Sorry Gina, are we hijacking your thread now?

[Paul M]

Without hijacking Gina's thread I'd just like to point to a thread I started sometime back. It's my own journey into entry level Pi. It might just help other novices who are still baffled by Linux, like me! 

Still,  I'm clinging to Gina's stomping entry into Pi land hoping that I can follow the proceedings.... 

[Gina]

No worries about hijacking my thread - I'm very interested, though it does fit better in another thread I've started in DIY Astronomer forum about using the RPi for controlling and capturing images.  I want to use the RPi for as much of my astro stuff as possible.  I'm dumping windoze and moving to Linux anyway and might as well go the whole hog

[Gina]

My poor old brain is overheating   I can see that this is good stuff.  My experience of the RPi is now 2 days   Or perhaps three.  I just need to slow down a bit.  When I was younger this would have been a breeze.  I'm remembering my Linux as I go along   Clearly all I want to do is possible and really pretty simple but with the brain power of a ZX81 complete with wobbly memory, I'm struggling a bit

[wimvb]

1 hour ago, Gina said:

[...]

Clearly all I want to do is possible and really pretty simple but with the brain power of a ZX81 complete with wobbly memory, I'm struggling a bit

TRS80 for my part, with just 4 k of memory, I believe it was.

That's right young'uns 4 kiloByte, plus an audio tape recorder for "hard drive"

Those were the days. But enough of this. I will check your other thread, Gina.

[psamathe]

20 hours ago, wimvb said:

...In the field it should also work with a mobile phone as a hotspot, but data transfer is very slow with this solution (at least it was when using a phone as hotspot in another application)...

One of the "challenges" I've had with my own playing around using my DSLR is image download time (I'm not auto-guiding or anything yet).  But for auto-guiders where the link speed to the client can be limiting Indi does have a feature called "Rapid Guide" where the guide star selection and guide camera image analysis is done within the CCD driver in the Ini server (i.e. remotely) and only positions are returned to the client i.e. no frame download.

Not used it (too much of a novice to be at auto-guiding) but might be useful to some.

I've still got more playing to get my own DSR image download issue sorted (better WiFi coverage, wider WiFi bands or local image storage on RPi).

Ian

[Gina]

I've been searching for RPi stuff for various control functions for my astro projects using the GPIO.

DS18B20+ One Wire Digital Temperature Sensor and the Raspberry Pi

Using PWM in RPi.GPIO
RPi.GPIO 0.5.2a now has software PWM – How to use it
PWM via DMA for the Raspberry Pi

Stepper Motor Control with the Raspberry Pi (YouTube)
How to connect Stepper motors to a Raspberry Pi
Stepper Motor Control In Python
Control Stepper Motors With Raspberry Pi: Tutorials and Resources

The stepper motor control is exactly the same way as I do it with the Arduino.

All this means that I can do all I want to with the RPi so no need for an Arduino or AVR chip.

[wimvb]

Just remember that the more you let the RPi do, the more processing power you take from it. Sometimes it's better to do the low level stuff by another device, such as an arduino. The RPi will then just issue commands to the other device.

[Gina]

Thank you for the warning   Most of the extra things I'm thinking of require very little computing power.  eg. focussing is only done occasionally and not at the same time as imaging.  PWM control could take more power but for heater control it only needs running very slowly. 

[wimvb]

On an avr such as arduino, dedicated timers are used for pwm. Pwm is done in hardware. On the RPi, this MAY be different. If pwm is done as a main process, it will tie up the main processor. I know too little about programming gpio on the RPi, but you might want to check this.

As for dew heater, I solved this the passive way, only using resistor to give 1 W of power from a 12 v battery.

[Gina]

Yes, I have only used on/off control for dew heaters in the past.  I don't think the amount of heat matters too much as long as it's sufficient.  I've heard it said that too much heat causes air currents which perturb the seeing but I've never found this myself.  I think automatic dew heaters are somewhat OTT.

[callump]

There's no reason why you could not use  a couple of RPi's - they can be chained for INDI control.

For powering a RPi you can power straight to the GPIO pins and not use the micro-usb.

/callum

[Gina]

Yes, that's what I intend to do.  I like the idea of using the GPIO pins for power - didn't know it there was any filtering or whatever between the micro-USB input and the GPIO pins.  Thank you

[callump]

I think the micro-usb is fused, and of course there is no polarity protection if you go straight on the gpio...

/callum

[wimvb]

If you want to use the RPi for various tasks, you may actually need more and dedicated RPis. The advantage of RPi is that they're cheap, small, and light weight, but pack a lot of power.

For direct hardware control, as in pwm, I think I would prefer arduino or avr. I did this with my dithering solution, very basic but it works for me.