Creating Kindle Serial Adapter

[Jarmex]

Hi all,

I am trying to re-use an old serial-USB cable I have lying around to interface with my KT2 Basic (which I have properly bricked, doh!)

The adapter I have is the AP1100R1 v1.2, which has a PL2303HXD chip.

The nice thing about this chip is that the VDD_325 on pin 4 supports a variable input:

RS232 VDD. The power pin for the serial port signals. When the serial port is 3.3V, this should be 3.3V. When the serial port is 2.5V, this should be 2.5V. The range can be from 1.8V~3.3V.

Currently it looks like it is hardwired to the VO_33, or the 3.3V input (i.e. I get continuity between pins).

From the AP1100R1 datasheet, it looks like I can get GND, TXD and RXD off pins 5, 3 and 2 respectively.

I think the battle plan is:

1. Break the connection between VDD_325 and VO_33
2. Connect cable from 1.8V output of the KT2 to VDD_325 for input (check voltage across TXD/RXD and GND to ensure 1.8V)
3. Connect pins 5, 3 and 2 off the existing DB9 connection to the corresponding terminals on the KT2.

My main questions are:

• Does this sound sensible?
• What would be the best way to break VDD_325 -> VO_33?
• What would be the best way to connect to VDD_325? The pins are minuscule and I have a pretty fat soldering iron
• Why do I not get continuity between RXD on the chip and pin 2 on the cable? I would expect to see this? (same with TXD and pin 5)

I have almost no knowledge of electronics apart from what I've read on these forums, so please let me know if I have misunderstood something!

Thanks for your help,

James

[knc1]

That is a multi-layer board, you are not going to easily re-wire it.

If you must hot-solder, invest in an appropriate sized soldering iron, it will be cheaper than a new motherboard for your Kindle.

We have directions, they are indexed by a Sticky thread here.
I'll save you a click or two:
https://www.mobileread.com/forums/sh...d.php?t=267541

Two things to note -
The directions include links to several different ways to make the serial port connection without using hot solder.

The directions include a link to the recommended adapter.
Which you can purchase from Amazon (who else?):
https://www.amazon.com/gp/product/B01GW2EGEK/ref=as_li_tl

You will also find a thread or two here about installing that adapter inside of a Kindle (a PW3, but should fit in a KT2).

[Jarmex]

Thanks for your reply knc1, appreciate your time in responding.

Unfortunately the suggested adapter costs quite a lot to ship to the UK as its only available in the US, so I was looking at lower cost options. As a one-off, it doesn't really make economic sense to spend $22.50 fixing a basic Kindle which doesn't cost much more than that second-hand!

I'm happy enough with the process of attaching the connections to the Kindle, as you mentioned there are quite a few posts (e.g. those linked in that article) and I have read around a lot, I'm really asking for advice on whether my plan to modify the existing serial adapter sounds like it would work!

If I understand it correctly, although it's a multi-layer board, the amount of rewiring is pretty minimal. I was thinking perhaps the easiest way to do it would be to cut the visible wire on the VO_33 output from the chip, then solder the 1.8v connection on to the visible wire of the VDD_325. The rest of the soldering can be done on the chunkier outputs of the DB-9 connection, although I'm still confused why there is no continuity between the RXD/TXD on the chip and RXD_RC and TXD_TC on the DB-9.

The only issue I can think of with the above solution is if the VO_33 output is used elsewhere on the chip, but I would imagine that's pretty unlikely?

Thanks again!

[knc1]

If you had read as far as Step two in the tutorial, you would have found:
http://jim.sh/ftx/
Then scroll down the page, open the "where to buy" spoiler.
There you can find places to order from the UK.

= = = =

You are really headed for trouble, trying "your way".

[Jarmex]

Originally Posted by knc1

If you had read as far as Step two in the tutorial, you would have found:
http://jim.sh/ftx/
Then scroll down the page, open the "where to buy" spoiler.
There you can find places to order from the UK.

= = = =

You are really headed for trouble, trying "your way".

Hi knc1, I hope I can assure you that I've read that tutorial and many other posts on this forum as well. In fact that 'international' Tindie link is exactly what I was talking about - if you look at the item plus shipping, it is the $22.50 that I referred to above!

Appreciate your comment about being headed for trouble, if it sounds like lunacy then I'll definitely scrap this plan of action, what would you see going wrong, providing I check before connecting that the outputs are definitely 1.8V?

Cheers

[Jarmex]

Has anyone got anything further to add? Thanks!