Why is your Juice4halt module so expensive compared to other UPS modules sold for the Raspberry Pi?
The main difference to a conventional UPS is that Juice4halt uses supercapacitors for storing energy instead of batteries. Charging and discharging supercapacitors requires a different circuit type, which is more complex due to an inevitable bidirectional DC/DC conversion. This fact makes the conventional UPS more suitable due to cost reasons.
However, the supercapacitors offer a much longer lifetime and a much wider temperature range making the whole UPS maintenance-free for the whole lifetime of the module. Together with a high reliability of the shutdown-boot handling, this fact presents the main strength of the Juice4halt UPS module.
What happens with the Juice4halt module if the power is restored while the Pi is shutting down? That is after the brownout period passes and shutdown is commanded, does the board cycle the power for restart if the power is restored?
When power comes back during a running shutdown process, the shutdown will be completed, and after that, the output will be turned off for about 2 seconds and then turned on again. This short turn-off and turn-on is inevitable to boot the Raspberry Pi again. During a running shutdown process charging of the supercapacitors is blocked.
Why doesn't the Raspberry Pi start booting immediately after plugging in the power supply?
To prevent the Raspberry Pi from crashing in case of a power failure occurring immediately after the start, it is important to first charge the supercapacitors and then to start the Raspberry Pi. Realize, that in case of a power failure occurring immediately after starting, the Juice4halt module must backup the whole boot and shutdown time. In other words, the Juice4halt module must be precharged to avoid crashing the Raspberry Pi due to early power failures.
There is a configuration option, where the Juice4halt starts immediately with the power supply start (look for Immediate start in the datasheet), but be careful: The immediate start is recommended only if the application can guarantee an uninterrupted power supply for the first moment when the supercapacitors are being charged.
We need to integrate your UPS module into our application, but the GPIO25 pin is already occupied by another task. Is there any solution for this problem?
Yes, there is a possibility to use the GPIO23 pin instead of the GPIO25 pin. For further information, please see the Application Note 171, You must also change the pin in the script files.
We were using an LCD display with Raspberry through standard 40pin FRC connector. However, your Juice4Halt reduces the number of pins to 26. Now, we do NOT know how to connect our LCD display.
You are right, our J4H boards reduce the number of pins to 26. As you can see, the body of the outer supercapacitor would collide with a 40 pin stacking header. In order to make use of the shape of the Raspberry Pi and positioning the supercapacitors very compactly, it was not possible to pass all 40 pins through from bottom to top.
You could use a 40-wire Flat ribbon cable with 3 crimped female connectors (similar to the Parallel ATA cable in personal computers) equipped with additional pin headers with long centered pins to allow transition from female to male. Probably you will have to crimp your own cable that will fit into your application. We don't sell any cable equipment.