Configuring Multiple Raspberry Pis

Hi Annie,

I’ll try to answer your questions.

How many laptops can a raspberry pi can realistically support?

Traditionally this has been between 10-15 but it’s hard to say without testing first. Using the latest model of the pi will help with user count. Connecting the pi to a wifi router to provide the Wifi while the pi is used only to provide RACHEL will greatly increase that count but can be more complicated to connect to and set up. If you’re looking to have more than 15 users connected in one classroom I would suggest looking at the RACHEL-Plus devices which can support many more users at once as it’s much more powerful rather than using multiple Pi devices. Two people I know have deployed the RACHEL-Pi recently are @giakonda and @SHOMI. Maybe they can help with their experiences with device counts.

Is there a way to set a limit to only have certain laptops join certain pis?

This is something I would like to make easier in the future. The easiest way to do this right now is to secure the wifi hotspot with a login and password that only certain users or laptops know and designate those laptops to use that hotspot. I’m not sure how familiar you are with this but I can help you with it if you’re interested. It requires changes to /etc/hostapd/hostapd.conf file on the pi.

In the event that one Pi shuts down how do we transfer those laptops connected to a new Rachel Pi server?

The Wifi Hotspot the RACHEL-Pi creates is open for anyone to connect to and access content. If one Pi shuts down they will be able to connect to another. If you add a login and password to the pis, they will need that login and password to connect to the new device/hotspot.

If you plan to use Kolibri, it can be set up as an open facility without the need to log in to access content but if learners use Kolibri to create their own user accounts and track learning, their profiles and progress will only be on the device they created their accounts with. If it shuts down they won’t be able to access their profiles on the new device they connect to. If they connect to another pi they will have access to the content on the new pi but they would have to create new Kolibri users to track progress. The Raspberry Pi can use either a Micro SD or USB device for storage. All of the content including RACHEL is contained on the storage device and can be used in another Raspberry Pi if one breaks.

Would we need a router if we have multiple raspberry pis in one school?

The Raspberry Pi devices act as individual devices that are separate from each other. You won’t need a router to have multiple running. To avoid conflicts between the wireless signals and make it easier to connect to you would need to change the Wifi SSID and channel in the /etc/hostapd/hostapd.conf file. This changes the name so you would have RACHEL-PI-01, RACHEL-Pi-02, etc.

I can help you with any of these changes if you decide to use multiple RACHEL-Pis. I would consider contacting someone from the RACHEL team to see if the RACHEL-Plus is more suited for your situation.

Hope that helps!

James

1 Like

Hi
I have used old broadband routers that are often thrown away as access points on a pi network of about 60 pcs and laptops however access was random at that time so the number or simultaneous users was much less than that. I bought several Synology servers ex-demo models from Synology at a very good price. Notes on how to do this are on giakonda.org.uk
The Synology servers handle over 90 pcs but they do need mains power to run. Most of our schools only have the solar power but in by us. That is 2x320 watt solar panels and 2 x 220 amp hr deep cycle batteries. The system provides power for charging laptops led lighting a good projector and of course charging phones.
Hope this helps.
Howard

2 Likes

I currently have 14 Raspberry PI desktops with 1 Raspberry PI RACHEL and 1 file server each using a 120gb SSD. I am using a $30 Linksys router from Walmart and I have decided to make static IP’s for each device. I want the person teaching the class to be able to use the VNC program to better assist several students without walking around the class all the time. I can set up other devices in groups and allow access as needed.

When I did my testing at home prior to deployment, I had a couple PI desktops running at least 15 instructional videos, Bino and Fino cartoons as well as pulling up the French Wiki. I did not have any issues during that time. I had also let the server sit idle for a day or 2 and then hit it hard and still no issues in performance.

I plan on adding 8 more desktops in August 2019. I may opt for another RACHEL and separate them via static IPs later. At least for a while, I do not see any immediate issues as I don’t anticipate a heavy load on the server with students looking up information for class assignments.

Our class has been running a couple days a week since January and from what I am hearing there are no issues. When the next school year starts in August, I will have a schedule put together with the faculty and ramp the class up since everyone will be used to the system and re-evaluate the performance and adjust as needed.

My class is all Raspberry PI’s, I like having Linux free software, small image files, a $50 desktop, and low power consumption since the class is 100% solar @ 400 watts (upgrading in Aug) and 960 amp AGM batteries.

With the PI’s being $30 each, I can keep several spares close by in case of failure and minimize the downtime. There are 500 students at the school so I need as many desktops as I can get.

3 Likes

Thanks you for your comments @giakonda and @SHOMI. It’s very interesting to see the details of your deployments. It sounds like the router is an important part of getting the user count up!

Hi James,
your hard work is what really makes the difference for us. I was worried that there was not going to be any more development on the new pi3+
We use the router if there is a building further than the range of the pi and as a dhcp server when there are pcs involved.
most of the schools we help don’t have any electricity so we first put in a solar system. Because are funfs are very limited this is not the system you would see on a house here in th UK but it does provide light and charges laptops and projector.
Each visit we make we write a short report saying what we. Have done. If you would like to read them they are on our Web side, giakonda.org.uk
I’ll also add the equipment we setup in more detail. Any critisisun would be welcome, it will help us improve what we do
Thanks again for all your help and efforts.
Kind regards Howard

2 Likes

@SHOMI do you use the pi network software that is provided on the pi?
Also I would be interested in any additional software you add.
Kind regards howard

Hi Howard,

Thanks for the information. I looked through your site and I think it’s great. The work you’re doing is amazing to see. I don’t have any criticisms but I am very interested in the details around setting up solar power and what is required to build a computer lab based on it as it seems necessary for rural deployments. I’m also curious if you’ve considered the Raspberry Pi 0 W for any use or if it’s too low powered to help. Thanks again.

James .

Hi James
I don’t know enough about the Pi0, Could I use the same image? If I could then I’ll try it out…
The power we supply is OK for 4 laptops projector pi router and 4 led strips. We could add more Pis but the monitors use a lot more power. If you had the money then having a bigger solar array say 10 panels and more battery capacity say 10 220Ah batteries could run a lab of 10 Pis.
You would have to figure in the desire of a village wanting to use some power for things like freezers which would inevitably be plugged in and could cause battery damage. We always run courses on system maintenance to try to overcome these issues. It costs us about £4000 to fix a school this could easily rum to £10000 if we included a lab. It is a difficult call but we decided to do more schools with what I regard the basic rather than fewer schools better equipped.
I intend to put up detailed calculations on energy use in the next few weeks.
Howard

1 Like

Howard,

My reasoning (often flawed).
Starting the class, I am just using a basic desktop image with a PI user (locked), a teacher account and a student account with browsers, Libre office, VNC and a few others for school work. I would like to introduce Scratch which is loaded but somewhat deemed a game by several right now.

I needed to be basic but have programs that will allow users to get acclimated and learn without being too overwhelmed. I opted for Linux over Windows is due to the viruses on most of the PC’s we encounter and potential cost of Windows. If something should go wrong, then the resolution needs to be quick and simple. I only need 1 Micro SD image and 1 of each server and can duplicate them with a USB writer, 5 min per sd or 60-ish per SSD. My laptop options have been a wide range of brands and age that I felt could be difficult being old and slow and could require too many OS images to keep track of.

I have thought about open ldap or the Pi-Net server to make user accounts and saving work more personal, as right know I just have a file server for the students to save work based upon grade and teacher. A lot depends on the teachers grasp.

With the school having 520 students, we decided to build a full-size classroom to better benefit this many students. This will allow us to see what does or doesn’t work and adjust as needed. Having a full class will provide others the opportunity to test drive it onsite and hopefully create new jobs that are so needed. We have a few on the Haitian team that are in school for IT and wanting to learn the system to gain extra computer skills, ability to run a lab, and teach the students and teachers at the school.

My issue right now is that this class is pretty much self-funded and I do 99% of the work. I can only make so many trips a year so I am trying to pick my battles.

Any feedback or suggestions are welcome. I certainly know that I don’t come close to having all the right answers.

Thanks,
Don

You are doing much the same as me! I guess there are no easy routes. I have put Raspbian as the o/s on laptops this with a 250Gb SSD seems to work well. I have been lucky enough to be given a lot of laptops all the same, Fujitsu lifebooks, old but very effective. it certainly makes cloning very easy.
I have put Calibre and Kolibri (with African Story book and Khan academy) on the laptops and RACHEL on the Pi. I also have GIMP and OpenShot on the laptops. Because of limited funds we have focused on installing solar power (up to 3 350watt panels) in several schools rather than focusing on one school. So far, (we have been doing this since 2014) we have done this in 17 schools. We have provided lots more with the Pi with RACHEL and powerbank,20000mA
I guess it’s mostly the teachers who use the equipment for class teaching.
Do you know of any low power 10 inch monitors?
Kind Regards
Howard

1 Like

Sorry @jamesk and @SHOMI
I forgot to include the @ bit!
Howard

@jamesk @giakonda Thank you so much for your replies! We are working to implement the Rachel Pi in Sierra Leone. I will definitely come back if we have any more questions.

Thank you for your reply!

Hi Howard,

The pi0 is the $5 USD version of the Raspberry Pi. Its very cheap and the size of half a credit card. You can build an image using a 2B, 3B, or 3B+ for use with the pi0w. I am putting up new images that are more suited for it as Kolibri requires too many hardware resources. I’m wondering if it has a use for deployments in remote areas as the power consumption and price are so low. I think it can handle 5 devices but it may be better for use with a couple of tablets.

Thanks for the info about solar panels. Very interesting stuff! I’m always looking to learn more so I can help find solutions. Monitors seem to be an issue all around as the cost is high as well. I’d like to look into the hardware side of things a bit more soon.

James

You’re welcome! If you have any questions in the future feel free to ask.

Thanks @jamesk
Am I correct in thinking if I take the sd card out of a pi3b+ and put it in a Pi0w it will work?
If this is correct and it can deliver RACHEL to 4 laptops that will be perfect for so many small, almost, villages.
I have not used the Pi 0 before.
If you come across any 10 inch displays for the Pi that are low power and cheap I would be very interested if you let me know.
Thanks
Howard

Hi Again @jamesk
Where can I find the images? Are they on the ftp site.
Kind Regards
Howard

Hi Howard,

You are correct. For now the best way to build an image for the Raspberry Pi 0W is to use another pi with an ethernet port to download the modules and then transfer that storage device to the 0w. I think it’s worth trying out to see if it works for your deployments. The power consumption should be significantly lower and the device is very cheap.

I have added images at the pinned pi images post here. The blue download button should show up when you go to the link for an image. I am having issues uploading to the FTP right now so hopefully that will be fixed soon.

Kolibri requires a bit too much CPU power to run on the pi0w so I suggest using the static or Kiwix images for it. There is a list explaining supported modules in the readme but basically those images don’t have KA-Lite or Kolibri. You can try any of the images out for testing with the pi0w though.

The pi0w can also boot from USB. It only has one Micro USB port, but you can use a USB OTG cable with your USB flash drive plugged into it. The only requirement is that you have a MicroSD with the file “bootcode.bin” on it. The file is very small so you can use a 512mb or 1gb card and it is only read once at boot time so it doesn’t have to be high speed. USB booting will speed it up.

What is the current cost of the screens you use, or are you using laptops exclusively right now?

James

Thanks James. I’ll get a few Pi0 and try them in June, our next visit.
At the moment we have Fujitsu laptops but I think a small lab of pis is worth a try.
to do this we would need low power screens. 10 inch would be a start.
Thanks for your help.
Kind regards Howard

You’re welcome Howard. Unfortunately the pi0w is not strong enough to operate as a desktop computer or it would be even more useful.

The cheapest place to source screens I have seen is always www.aliexpress.com but it may take some time and the quality varies. I am starting to look into this problem more so I’ll let you know if I find a good solution.

James