Objectives:

The goal of this project and the other projects listed below was to create a self contained Prusa i3 Printer withMMU2 including anOctoPrint wireless print server. The printer and print server must power up and down in response to the printer's power switch; that is theprint server must not require a separate power switch.

The other parts of this project are documented here:

• 12/24Vdc to 5Vdc USB A buck converter

https://www.thingiverse.com/thing:4167242

• PSU Cover with Access Door

https://www.thingiverse.com/thing:4153686

• Bear Printer Structure upgrade

https://www.thingiverse.com/thing:2808408

Overview:

TheOctoPrint Print Server with UPS HAT consists of either aRaspberry Pi 3A+ or3B+ computer along with aPi Shop UPS HAT mounted on a V-Slot channel most commonly found on thePrusa I3 MK2 orMk3 series printers withBear Upgrade installed.

The RPi 3A+ is a smaller package but includes only one USB and no Ethernet port. It is most suited where space is an issue and the device is used primarily forOctoPrint.

The RPi 3B+ is larger and includes 4 USB and one Ethernet ports.

The Print Server is intended to be powered by the Printer PSU via a 12/24Vdc converter. See above.

ThePi Shop UPS powers the RPi for short periods of time following printer power off or loss of utility power. By default the period is set to 60 seconds but can be adjusted for longer intervals. At the end of the power loss interval, the RPi is commanded to power down gracefully thus preventing software corruption due to abrupt power failure.

The UPS will command a reboot of the RPi upon power restoration without any user intervention.

The UPS connects to the RPi via the GPIO only. No external connections are required. Print server power is via the RPi micro USB Power Port. The RPi power supply must be capable of 5.1Vdc at 2A although in normal operation current draw is rarely above 1A.

Assembly

1. Place the UPS Battery side down on the Upper case,
2. Screw 4 standoffs into the Upper case through the holes in the UPS HAT,
3. Insert the RPi GPIO pins into the UPS GPIO sockets,
4. Place the Bottom case over the RPI and fasten the two halves of the case using 4 flat head counter sunk M3 machine screws,
5. Install Octoprint Software per https://octoprint.org,
6. Install and configure Pi Shop UPS HAT software per the included Word Document.

Print Settings

Printer Brand:

Prusa

Printer:

i3 MK3 MMU 2

Rafts:

No

Supports:

No

Resolution:

.025

Infill:

20%

Filament: AmazonBasics PTEG

Orange How I Designed This ===================

General

TheOctoPrint Print Server consists ofTop andBottom 3D printed parts,Raspberry Pi 3A+ orRaspberry Pi 3B+ computer, and aPi Shop UPS HAT. Both RPi computers use the same processor and therefore offer the same performance. Both support WiFi. Only the 3B+ contains a Wired Ethernet port. The 3A+ contains 1 USB port whereas the 3B+ has four.

STL files are included for both computers. Select the appropriate Top and Bottom pair for the computer being used.

The Cases support mounting on V-Slot rails but can but used in stand along condition as well.

ThePi Shop UPS HAT connects to the RPi via the GPIO pins (5V, Gnd, GPIO 17, 18, and 27). No other connected is supported. The UPS battery is recharged through the GPIO 5Vdc power pins. These same pins supply power to the RPi when external power is not available.

The battery supplied with the UPS is a Lithium with a capacity of 450mah. Any 3.7V rechargeable lithium battery will suffice as long as its physical size fits into the case. The supplied battery is sufficient to support graceful RPi shutdown when power us removed from the RPi.

Attached is a Word document explaining the UPS's Theory of Operation and Setup including software load and configuration. The latest version of this document is posted here:

• https://www.pishop.us/raspberry-pi-ups-hat-guide/

UPS Selection Criteria

TheRaspberry Pi (RPi) is a traditional stored programLinux (Raspbian) programmed digital computer. Unlike the Arduino family of microprocessors the RPi supports a robust file system that needs flushed before power down. Failure to do so can, and often does, corrupt files requiring the system to be reloaded, somethings from scratch. Hence the need to power the RPi long enough to allow it to shutdown properly and some method to signal the RPi software that power has been lost.

The following requirements for the OctoPrint UPS have been established:

1. UPS must be small enough to fit into a typical RPi case,
2. The UPS must be able to sense RPI power loss and provide uninterruptible power for at least as long as it would take to gracefully shutdown the RPi,
3. UPS must automatically (without manual intervention) power up and reboot the RPi once power has been restored,
4. The UPS must be reasonably priced (not to exceed the cost of the RPi),
5. RPI Camera flat cable must be able to be routed outside the case without modifying either the RPi or the UPS,
6. The UPS must be compatible with both the RPI 3A+ and 3B+ computers.

UPS Reviewed

A large number of possible UPS were reviewed for possible selection. Many were discounted for form factor which required larger cases than desirable. Others were rejected because they were not available for immediate purchase.

Three UPSs made the final cut. They Were:

1. Pi Shop UPS HAT
2. PI Juice UPS HAT
3. Geekworm (MakerFocus) UPS HAT

UPS Discussion:

See Choices below:

Greekworm/MakerFocus

The Geekworm a/k/a MakerFocus RPi UPS HAT is reasonable priced and relatively available from Amazon, Banggood, Geekworm, and others. The price is generally in the mid $20USD range.

Its form factor is the size of the shorter 3A+ and can charge and supply power to the RPi at the same time. This UPS has a separate micro-USB power port which allows it to recharge the battery even if the RPi is powered off. There is no cutout for the RPi Camera cable but it does leave sufficient height to route the cable out the back side over the USB connector(s).

This UPS provides battery voltage and capacity to the RPi software via the I2C interface which makes it possible to have a "Fuel Gage" to indicate remaining run time, etc.

This UPS was subject to considerable testing and was finally rejected because the UPS must be powered on manually if power was lost momentarily. In this case the UPS continues to supply power to the RPi but unless the RPi is completed shutdown it will not automatically reboot on power restoration and the battery will not recharge unless the UPS is manually reset.

Pi Juice from Pi Supply

This is undoubtedly the most capable RPi UPS HAT and is available through several distributors. Allied Electronics lists the price at $64.99. The UPS may well be worth high relative cost but it is outside the range for this project. Most of the extensive features and software would go unused in this application.

Pi Shop

This UPS is reasonable priced and available directly from Pi Shop in the US. It does not have any means to report the battery status but does automatically begin charging the battery and rebooting the RPi when RPI power is restore. I2C interface is not used for battery status so there is no way to know how much run time is available on power loss. Price from Pi Shop is $29.95USD, the upper end of the acceptable range.

No external connection is needed or available to power the UPS HAT, it takes power from the GPIO pins and uses these same pins to provide 5Vdc to power the RPI on power loss.

The only power connection is via the normal RPi micro-USB connector.

Pi Shop UPS does have a Camera Cable slot cut in the UPS HAT Circuit Board allowing the cable to be routed directly out of the case side.

BOM

Raspberry Pi 3A+ https://www.amazon.com/Raspberry-Pi-Model-A-256MB/dp/B00PEX05TO

Pi Shop UPS HAT https://www.pishop.us/product/raspberry-pi-ups-hat/

M3x16 Male/Female Standoffs https://www.amazon.com/100pcs-Standoff-Spacer-Replacement-Female/dp/B07GCXG54X

M5x10 flat head screws https://www.amazon.com/M5-0-80-8mm-Stainless-Countersunk-MonsterBolts/dp/B078YXRPSF

M3x10 Flat Head Screws: https://www.amazon.com/gp/product/B073J4CRZV

Category: 3D Printer Accessories