As someone who worked on kindle power consumption many years ago: One of the (by far) biggest consumers of power is the WiFi connection. It has to wake up and respond to the AP in order to not get disconnected every x seconds.
Off the top of my head, I think 'on' average power consumption was ~700uA without wifi, and about 1.5mA+/- with Wifi. This is from over a decade ago, so my memory is fuzzy though...
Obviously, page changes used relatively large amounts of power. I don't recall the exact amounts, but it was 100s of mA for seconds.
There is also an "every x pages, do a full screen refresh (black to white)" to fix up the ghosting issue that the article writer saw.
For the less reverse-engineering prone among us, there are also similarly sized e-ink displays that plug into Raspberry Pi DSI ports for maybe $5 more on Aliexpress. They might actually be salvaged kindle screens.
I love using Kindle's as single purpose tablet/interfaces/displays. I'm the weirdo who actually prefers the LCD displays vs eInk and it's incredibly easy to set Kindle Fire's into dev mode which lets you display a webpage, never turn off while connected to power and never show ads.
You can regularly find the Kindle Fire HD10s for ~$40
Good to know about Kindle Fire. And hah, I can totally see why you'd prefer LCD's over e-ink - no ghosting + readable in pitch dark would be a sweet upgrade to the dashboard.
I was glad to see the note about battery life down at the bottom. My biggest challenge with the old Kindles I have laying around is that most of them won't hold a charge!
I haven't developed on the Kindle ecosystem, but with old Nook devices I am able to set a screensaver, alarm, and put the device into deep sleep between refreshes. This changed my battery life from ~48 hours into 30+ days of battery life even with some old devices.
The "electric sign" app does this, which is where I referenced the code.
With trmnl, the image only refreshes every 10 mins so the device will set a ~9 minute alarm to wake the device right before it needs to load the next update.
The refresh period is also configurable so a slower refresh interval (e.g. every hour for less time-sensitive screens) yields larger battery savings
Yeah that was definitely a worry of mine before I booted it up. Luckily it's still got decent battery life. We'll see how it holds up in 6 months...
Dyson vacuums and Kindles are not the same whatsoever, but I wonder how easily it'd be to swap out the battery on an older Kindle. For our vacuum, all I needed was a 20 dollar replacement battery and the will unscrew 3 mini screws.
One thing that's disappointed me is that despite all the excitement over better and cheaper battery technology, you can't buy a cheapish drop in replacement battery for e.g. an old kindle that has more storage capacity than the OEM version.
I understand there's like all sorts of complexities in standards, form factors, voltage, wattage, etc, but I really wish I could upgrade my old devices like that.
Why Jailbreak the Kindle when you can just open its browser and visit a website that shows the arrival times?
The Kindle browser is surprisingly decent, I made Claude Code generate an RSS feed reader compatible with the Kindle browser, with the ability to read full articles (for those feeds that require you to visit the website), and download articles. It also supports Reddit and Google News RSS feed. This is my new favorite way of browsing the internet.
As someone who worked on kindle power consumption many years ago: One of the (by far) biggest consumers of power is the WiFi connection. It has to wake up and respond to the AP in order to not get disconnected every x seconds.
Off the top of my head, I think 'on' average power consumption was ~700uA without wifi, and about 1.5mA+/- with Wifi. This is from over a decade ago, so my memory is fuzzy though...
Obviously, page changes used relatively large amounts of power. I don't recall the exact amounts, but it was 100s of mA for seconds.
There is also an "every x pages, do a full screen refresh (black to white)" to fix up the ghosting issue that the article writer saw.
Kindles are fun devices to hack and play with. I can grab an old kindle for €15-20 on eBay.
I did the same last year and had lots of fun in the process.
https://samkhawase.com/blog/hacking-kindle/
Can you start jailbreaking straight away, or does it require an internet connection and Amazon account first during setup?
For the less reverse-engineering prone among us, there are also similarly sized e-ink displays that plug into Raspberry Pi DSI ports for maybe $5 more on Aliexpress. They might actually be salvaged kindle screens.
Do you have a model number or link, please?
I love it! Always fun to see the route somebody else took to get to the same end product.
Your post is making me want to try more Cloudflare Developer Platform stuff like Cloudflare Workers.
I love using Kindle's as single purpose tablet/interfaces/displays. I'm the weirdo who actually prefers the LCD displays vs eInk and it's incredibly easy to set Kindle Fire's into dev mode which lets you display a webpage, never turn off while connected to power and never show ads.
You can regularly find the Kindle Fire HD10s for ~$40
Good to know about Kindle Fire. And hah, I can totally see why you'd prefer LCD's over e-ink - no ghosting + readable in pitch dark would be a sweet upgrade to the dashboard.
I was glad to see the note about battery life down at the bottom. My biggest challenge with the old Kindles I have laying around is that most of them won't hold a charge!
I haven't developed on the Kindle ecosystem, but with old Nook devices I am able to set a screensaver, alarm, and put the device into deep sleep between refreshes. This changed my battery life from ~48 hours into 30+ days of battery life even with some old devices.
The "electric sign" app does this, which is where I referenced the code.
With trmnl, the image only refreshes every 10 mins so the device will set a ~9 minute alarm to wake the device right before it needs to load the next update.
The refresh period is also configurable so a slower refresh interval (e.g. every hour for less time-sensitive screens) yields larger battery savings
Yeah that was definitely a worry of mine before I booted it up. Luckily it's still got decent battery life. We'll see how it holds up in 6 months...
Dyson vacuums and Kindles are not the same whatsoever, but I wonder how easily it'd be to swap out the battery on an older Kindle. For our vacuum, all I needed was a 20 dollar replacement battery and the will unscrew 3 mini screws.
One thing that's disappointed me is that despite all the excitement over better and cheaper battery technology, you can't buy a cheapish drop in replacement battery for e.g. an old kindle that has more storage capacity than the OEM version.
I understand there's like all sorts of complexities in standards, form factors, voltage, wattage, etc, but I really wish I could upgrade my old devices like that.
For some reason, this project reminds me of this one:
https://engineersneedart.com/systemsix/systemsix.html
Woah this is really cool! Makes me want to create a custom mount
Why Jailbreak the Kindle when you can just open its browser and visit a website that shows the arrival times?
The Kindle browser is surprisingly decent, I made Claude Code generate an RSS feed reader compatible with the Kindle browser, with the ability to read full articles (for those feeds that require you to visit the website), and download articles. It also supports Reddit and Google News RSS feed. This is my new favorite way of browsing the internet.
https://github.com/adhamsalama/simple-rss-reader
It's easier to load up a page in the Kindle browser, but more fun to jailbreak :D
I also didn't want the browser bar at the top.
Fair enough. I did consider jailbreaking my Kindle but I am afraid of bricking it.
Also fair - bricking it was definitely one of my main concerns.
After going through this process though, I'd say as long as somebody has basic linux knowledge, chances of bricking are pretty low.
A little bit of a hijack, but it's hard to find a more relevant time to post this.
For a defunct startup, I built this exact thing as a product for coffee shops:
cafetren.com.ar
https://cafetren-com-ar.translate.goog/?_x_tr_sl=auto&_x_tr_... (translated from spanish):