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Author Topic: The Slatiq Project - or "please help an idiot with a soldering iron"  (Read 9557 times)
Aerendraca
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« Reply #15 on: February 17, 2015, 07:59:01 PM »

Ok this is good, we're getting somewhere. I would get some solid core 0.6mm diameter (~22awg) wire, and I would probably cut and use the cable you have since you're in the envious position of having the cable with the connector attached. I'd solder directly to the wire and use some 1mm heatshrink to insulate the connection.

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brunobarbosa
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« Reply #16 on: February 17, 2015, 10:16:37 PM »

All done!

tested for continuity and it is up and running!

Now i have 3 remaining wires - pins 2, 3 and 11. It seems like for the teensy, only 2 wires are required - Rx and Tx. Would it be safe to test these now?
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Aerendraca
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« Reply #17 on: February 18, 2015, 07:34:29 PM »

Ok, I have an idea, lets see if the USB part of the chip is actually activated, you might not need the teensy at all!

Here's the pinout for the MN101EF35D chip.


* MN101EF35DPinout.jpg (154.34 KB. 790x772 - viewed 176 times.)


Pins 39 and 40 of the chip are the USB data pins (D+ and D-), my suggestion is to see if you get any continuity between these pins and any of the pins of the connector. Chances are you wont but its worth a go.

If you do see continuity this could be good news although you may need to step the voltage of the USB socket down to 3.3V to get this working properly.

If you don't see any continuity with these pins try pins 12 and 13, and pins 35 and 36. These four pins are means for the chip to connect via serial com. If you see continuity with any of these then we know where to wire the Teensy (almost).

« Last Edit: February 18, 2015, 07:41:14 PM by Aerendraca » Logged
brunobarbosa
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« Reply #18 on: February 18, 2015, 10:40:50 PM »

OK, so these were the findings I had with the multimeter. I'll make a diagram to make it easier to follow:

Chip ---------- Connector --------- Value
39     ---------------- 3 -----------------  020
39     ---------------- 2 ------------------ 480
40     ---------------- 3 ------------------ 480
40     ---------------- 2 ------------------ 020
12     ---------------- 2 ------------------ 700
13     ---------------- 3 ------------------ 700
35     ---------------- 2 ------------------ 700
36     ---------------- 2 ------------------ 700


I am a little confused with these values, as normally, whence checking for continuity this multimeter drops to 000 if there is continuity.
Also, any other combinations like 36 to 3 produced no value.

Does this seem normal?
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Aerendraca
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« Reply #19 on: February 18, 2015, 11:44:02 PM »

I'm a little tired so I need to think about this a bit, but it would seem that pin 39(chip) is connected to pin 3(connector) and pin 40 (chip) is connected to pin 2 (connector). I think this might work visa USB. The reason for obscure values is because the pins are not directly connected to the socket, they passed through other components which have various properties.
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Aerendraca
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« Reply #20 on: February 19, 2015, 12:37:50 AM »

Ok I've had a bit more of a think and I reviewed you're photos of the digitizer PCB. If you look at the photo of the digitizer PCB you can see two black components between the connector and the white printed letters "C2" (or capacitor 2), on these you can see the markings "200", which in surface mount (smd) speak is 20ohms - 020 continuity value ringing any bells? - no coincidence I'm sure.

One last thing to check then. If you check continuity from pin 39 to the right side of the lower (as per the image) resistor do you get all zeros? If you try the same with the upper resistor and pin 40 do you get all zeros?

If you answer yes to both of these I think we can safely say you're digitizer uses USB communication at 3.3v, and more than this we have a pinout.
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brunobarbosa
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« Reply #21 on: February 19, 2015, 12:40:36 AM »

Give me a second and I'll test this, I was just logging in again!

-- EDIT --

It is confirmed, we have continuity with those two resistors!

So this means that i can use a regular USB cable, provided can get it to output only 3.3v instead of 5v.

I have a couple of spare regulators that i purchased for the teensy (link below). Do you think these will be of any use for this?

https://www.pjrc.com/store/mcp1825.html


« Last Edit: February 19, 2015, 12:50:06 AM by brunobarbosa » Logged
Aerendraca
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« Reply #22 on: February 19, 2015, 09:03:39 AM »

In principle yes you should be able to use USB.

Also, yes you can use that voltage regulator however, you will need to get a couple of additional components from somewhere; don't worry they're super cheap and easy to find.

You will also need:
1x 4.7uF ceramic capacitor
1x 1uF ceramic capacitor

The circuit is really simple so don't let the additional components put you off. I'll try and draw up a simple circuit today for you to follow.
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brunobarbosa
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« Reply #23 on: February 19, 2015, 11:52:46 AM »

Thanks!

Will only ceramic capacitors work or will electrolytic or polyester ones work as well?
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Aerendraca
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« Reply #24 on: February 19, 2015, 12:15:22 PM »

This is what the datasheet has to say about it:

Quote
4.3 Output Capacitor
The MCP1825/MCP1825S requires a minimum output
capacitance of 1 μF for output voltage stability.
Ceramic capacitors are recommended because of their
size, cost and environmental robustness qualities.
Aluminum-electrolytic and tantalum capacitors can be
used on the LDO output as well
. The Equivalent Series
Resistance (ESR) of the electrolytic output capacitor
must be no greater than 1ohm. The output capacitor
should be located as close to the LDO output as is
practical.

And the input capacitor (4.7uF):

Quote
4.4 Input Capacitor
Low input source impedance is necessary for the LDO
output to operate properly. When operating from
batteries, or in applications with long lead length
(> 10 inches) between the input source and the LDO,
some input capacitance is recommended. A minimum
of 1.0 μF to 4.7 μF is recommended for most
applications. For applications that have output step load
requirements, the input capacitance of the LDO is very
important. The input capacitance provides the LDO
with a good local low-impedance source to pull the
transient currents from in order to respond quickly to
the output load step. For good step response
performance, the input capacitor should be of
equivalent (or higher) value than the output capacitor.
The capacitor should be placed as close to the input of
the LDO as is practical. Larger input capacitors will also
help reduce any high-frequency noise on the input and
output of the LDO and reduce the effects of any
inductance that exists between the input source
voltage and the input capacitance of the LDO.

So actually there is no specification that the input capacitor should be ceramic either, I would suggest then that electrolytic capacitors will be absolutely fine for this application.

By the way, LDO just stands for Low Dropout. To quote Wiki -
Quote
A low-dropout or LDO regulator is a DC linear voltage regulator which can regulate the output voltage even when the supply voltage is very close to the output voltage.
« Last Edit: February 19, 2015, 12:18:22 PM by Aerendraca » Logged
brunobarbosa
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« Reply #25 on: February 19, 2015, 02:50:19 PM »

Thanks! I'm going to ser if i can get my hands on those after work today!
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Aerendraca
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« Reply #26 on: February 19, 2015, 08:56:41 PM »

Ok here's the very simple diagram from the step-down to 3.3V.


* USB3.3V_Stepdown.jpg (78.27 KB. 896x508 - viewed 169 times.)

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brunobarbosa
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« Reply #27 on: February 19, 2015, 09:18:17 PM »

Thanks! At the risk of sounding stupid, the ground wire from the USB and the ground wire from the board conector should connect to the GND you indicated on the drawing, or elsewhere?
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Aerendraca
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« Reply #28 on: February 19, 2015, 10:26:26 PM »

Yep that's correct. Good luck! Fingers crossed.
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brunobarbosa
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« Reply #29 on: February 20, 2015, 12:00:56 AM »

I can't than you enough for your invaluable help, you have been a true lifesaver through this whole thing! Sadly I wasn't able to get the capacitors today, I'm going to try and get them tomorrow and see if I can have this puppy working by the weekend!
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