Re: PCB designer? Weight issues.

Jared Smith
 

My charge controller boards have arrived and they actually work - despite my soldering skills! Photos are attached.

I'll probably design a second version with a few minor modifications - mostly a smaller Schottky diode, bigger pads for that pesky Inductor (the L1 silver component near the top left), and better labelling.

This charges the supercapacitor to 5.2 volts from only a couple small .5v solar cells. I now need to determine how many solar cells I need to provide sufficient current for the 2 minute transmission. My current draw is 3-5mA when idle, 35mA during GPS acquisition, and 42 mA when transmitting.

I hacked around the issue of the transmitter interfering with the GPS. I added an NPN transistor to act as a switch to use the Arduino to turn the power on to the transmitter only when it's needed. Unfortunately, when I turned it on, the interference kicked the GPS out of sleep mode (jumping it from 5mA to 30mA, or 70+mA for everything). So I added a second switch to turn the GPS off when it's not needed. This adds a bit of weight and requires a longer cold boot GPS fix every 10 minutes, but that shouldn't be an issue at 40,000 feet.

If I can get the antenna set up and everything tied together, I might see if the USU folks will let me fly one on one of their balloons this Saturday.

Jared


On Thu, Jul 6, 2017 at 10:25 AM, Kevin Reeve <kevin.reeve@...> wrote:
Jared,

I have a temp controlled soldering station that includes the heat gun for SMD work/rework, and various tip sizes.  I also have some awesome indium solder. You are welcome to use it.

 There are some great SMD solder videos on Utube.  Some use solder paste across the pads, hold the component with tweezers and heat it up with the heat gun and push in place.

Kevin


From: <BARC-HAB@groups.io> on behalf of Josh Jensen <kd7wrc@...>
Reply-To: "BARC-HAB@groups.io" <BARC-HAB@groups.io>
Date: Thursday, July 6, 2017 at 10:14 AM
To: "BARC-HAB@groups.io" <BARC-HAB@groups.io>
Subject: Re: [BARC-HAB] PCB designer? Weight issues.

Jared,

0603 components aren't that bad to solder. It's when you get down to 0402 size that they get to be a pain. 

Josh

On Jul 6, 2017 09:46, "Jared Smith" <jared@...> wrote:
After realizing the previous charge controller wouldn't work, I decided to design my own. The schematic and PCB renders are attached. This uses the SPV1040 charge controller - http://www.st.com/en/power-management/spv1040.html - and is generally based on their example board - http://www.st.com/resource/en/application_note/cd00292052.pdf

The board is very small - only 1 inch X .5 inches. The components are mostly tiny 0603 size - so should be a fun challenge to solder. The IC is 3mmX4.4mm.

The S+/- pads are for the small solar cells. I should be able to use 2 of them in series to make ~1.2 volts. The circuit then upconverts this to 5 volts which charges the supercapacitor (CAP+/-) which functions as a battery (except this one works at -40 degrees). It then routes back to V+/- which will go to the Arduino raw power input. Most of the capacitors and resistors are used to set the controller charge values.

There's also a voltage divider on the output that goes to the A connector. This will allow me to measure the output voltage from the Arduino so I don't transmit or turn on the GPS if the voltage is too low.

Feedback or criticism of the design is VERY welcome. I figure I have around 50/50 odds that I designed this in a way that will actually work. I'll order up some PCBs from OSH Park soon and give it a go.

Thanks,

Jared



On Wed, Jun 28, 2017 at 8:06 AM, Jared Smith <jared@...> wrote:
Thank you Brandon.


I'll put together a GitHub repository for the code and will share it soon. You won't really be able to test it without the hardware, but I'm happy to share it.

The charge controller didn't work as expected. The idea was good (the board was only .6 grams), but I didn't realize that the IC has an input current limiter of 100mA. With the voltage upconvert (1.5v converted to 4.2v), this decreases current and didn't leave enough to keep things running. By the time I added enough solar cells to maintain adequate current, it no longer provided a weight saving to use the charge controller. I'm looking at different options - or just might go with a slightly smaller solar cell and run 8 or 9 of them.

I've been testing everything and it seems to work great. I have it sitting out in the sun this morning to see what happens in marginal solar conditions as the sun comes up. The WSPR mode is incredibly efficient - it was heard in Florida on 10 milliwatts last night. The new, smaller clock generator should be here in a couple weeks, then I think I'll have most everything necessary for a launch.

Jared




On Tue, Jun 27, 2017 at 11:48 PM, Brandon Tibbitts <Tibbs327@...> wrote:

Yep, that sounds like you're on the right track. I'll keep my eye open for thin PCB options, and once everything is proven out, then could help put it all to one thin/tiny PCB. As you mentioned that is key for longer term reliability.

Simple GPS antenna work better horizontal, but not entirely deaf while vertical either..

Do you have a system/component overview? Or did I miss it somewhere. Also were you archiving the code somewhere?

Brandon



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