Rev X1 Buildout

[NZ0I]

I've started populating the Rev X1 boards. As expected in an experimental board, there have been some issues discovered, but nothing too serious. As I find problems (mostly minor footprint misfits thus far) I update the board design to ensure they will not happen again. I will do the same for any schematic issues.

80M ANTENNA BOARD

I started out working on the 80m Antenna board. So far I've only installed the main loop: 1 Turn of RG-214 Mil Spec coaxial cable, 71cm long, with 2.5 cm jacket removed each end

(the silver-coated shield is the antenna conductor). I also installed C501 and C502 and tuned the loop to resonance as indicated by an MFJ antenna tuner, loosely coupled to the loop antenna. I then wired the coupling loop directly to the BNC connector and plugged it into a GC receiver tuned to the lower end of the 80m band. Immediately I heard a full scale W1AW signal. The tuned loop appears to be adequately sensitive, but no performance measurements yet.

I went in search of some brazing rod for the sense antenna. Local stores I went to no longer sell uncoated bronze brazing rod, but at Lowes Home Improvement I found a 36-inch length of bronze rod for sale at a reasonable price. So the sense antenna has been installed as well, but none of the other circuitry is in place, so the sense antenna is not yet functional. The remaining components are truly experimental, and a good deal of trial and error will be required to determine the best way to wind the transformer that combines the tuned-loop signal with the sense antenna signal, and adjusts their relative phase and amplitude.

CONTROL HEAD BOARD

I'm populating the Control Head before the receiver and interface boards because it also serves as the power supply for the rest of the Receiver Development Platform, and because the LCD will serve as an essential piece of test equipment for debugging as assembly continues.

The LiPo charger and LiPo protection circuit, and the 7.5V switching supply have been built and tested, and they are functioning as expected. The LiPo protector hasn't been carefully tested to ensure that it limits battery current or under/over voltage at the right levels. But the undervoltage protection function has been shown to be operational: all you have to do is remove the LiPo battery, which the protector interprets as a low battery voltage condition, to have the protector isolate the battery from discharging further. The way this protector works, it will never allow the LiPo to be further discharged until it detects that a charger has been plugged in. So once you unplug the LiPo, plugging the LiPo back in will not apply power to the unit, even if the LiPo is fully charged. You must first plug a charger in, if only for a few seconds, and then the protector will once again allow battery current to flow even after the charger is removed.

Diodes Incorporated sells a version of the LiPo protector which will automatically re-enable discharging a charged battery, without first requiring the application of a charger. But DigiKey does not sell that version of the chip except in quantities of 3000 or more. But I think the spec'd version will suffice in this application... but one must remember not to unplug the LiPo unless a charging source is available, otherwise the Control Head will be inoperable. But even a juice pack plugged into the external micro-USB port will serve as a re-enabler.

[Patrick Robert Sears]

Hi Charles,

It's super to see the progress going on.  Can't wait for more  :  )

Cheers,

Patrick

--
You received this message because you are subscribed to the Google Groups "Receiver Development Platform" group.
To unsubscribe from this group and stop receiving emails from it, send an email to receiver-development...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/receiver-development-platform/edaa71f8-9961-4637-9afa-73a7c6c28497%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[NZ0I]

I discovered yesterday that I specified a poor choice for the diodes in the power turn-on circuit. A very important parameter is the leakage current. We are using very high value resistors in that circuit in order to minimize battery drain while the headphone is unplugged. So even a fairly small diode leakage current (~100 uA) is enough to cause a significant voltage drop across such a high impedance. Getting the leakage current down below 10 uA is more important than other specs, like the forward voltage drop. And since leakage current increases with temperature, it will be a good idea to get the room temp leakage down to around 1 uA.

Fortunately, suitable parts are available with the same footprint size and pinout, and for a cheaper price than the wrong-choice parts. I'll just need to place another DigiKey order.

[Gerald Boyd]

Charles,

This is real good progress it's all coming together.

The 80 meter assembly looks robust  and compact. Looking forward for  testing results on it.

Some years ago I got some brazing rod for making the foxfinder sense antenna from a local welding supply. Will look in fixfinder notes to see if I still have the invoice to get a part number. It came in about 3 foot lengths. Still have a bag of them.

If I can find the part number can call and see if it is still in stock.

Also used them for the Doppler antennas for the mobile DF.

Is there any help you need?

Jerry

Sent from my iPad

--
You received this message because you are subscribed to the Google Groups "Receiver Development Platform" group.
To unsubscribe from this group and stop receiving emails from it, send an email to receiver-development...@googlegroups.com.

To view this discussion on the web visit https://groups.google.com/d/msgid/receiver-development-platform/bcab5dd0-faf3-43d1-8a94-688265996fd5%40googlegroups.com.

[Charles Scharlau]

Hi Jerry,

I thought I'd play around with the 80M antenna some more, and see if I can get a good first cut at the windings for its transformer. While I'm waiting for the replacement parts from DigiKey might be a good time to mess with the 80M antenna again.

I ordered just enough RG-214 to build three of the 80m antennas. Once I've got an approximate transformer design working, I thought I'd install the main loop on a couple more boards and send one to you. That way you and I can work with nearly identical units, and can compare performance and notes knowing that the main loops are basically identical. I've also got enough of the other antenna components, including the toroid, so I can send along most of the parts you'll need so there shouldn't be much you'll need to order.

Does that sound OK to you?

To unsubscribe from this group and stop receiving emails from it, send an email to receiver-development-platform+unsub...@googlegroups.com.

[Gerald Boyd]

Yes that sounds real good.

Jerry 

Sent from my iPhone

[NZ0I]

The first Rev X1 Control Head is alive and well:

The switch visible at the top is a temporary on/off solution: the switch plugs into a header for the cable that will attach to the Digital Interface board. A few "blue wires" and minor modifications were required in order to get the Li-Ion charging and protection circuits to play nicely together while powering the switching supply. As shown in the photo, the display is working. Also the Control Head is running off of a LiPo battery, so all the power supply circuitry is working. The headphone off/on circuit draws less than 4 uA while shut down, about 30% less than previous measurements, possibly because of the low-leakage diodes now being used. The real time clock has not been tested yet, and the digital compass module has not yet been installed. 

On Saturday, March 18, 2017 at 9:41:07 AM UTC-4, NZ0I wrote:

[Gerald Boyd]

That's awesome.

Jerry

Sent from my iPad

--
You received this message because you are subscribed to the Google Groups "Receiver Development Platform" group.

To unsubscribe from this group and stop receiving emails from it, send an email to receiver-development...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/receiver-development-platform/a89ea6cc-4fb4-4313-91ff-7e18be334dfe%40googlegroups.com.

[NZ0I]

More progress:

I've got a Digital Interface board built, and running its processor while attached to the Control Head. Now, instead of sharing the I2C bus, the Digital Interface processor has its USART attached to the Control Head USART. The Digital Interface is sending the alphabet, one character every 500 ms, to the Control Head at 9600 baud and the Control Head is printing the characters it receives to the display.

After placing the PCB order with OSH Park, I came to realize that the USART needs to be the primary inter-processor communication bus. There are several advantages to this: (1) Simplicity - the USART is going to be simpler to utilize in software than the I2C bus; (2) By keeping the I2C buses on each board isolated from the I2C bus on any connected boards, we will have fewer issues with I2C bus address conflicts (we can use identical I2C parts on connected boards); (3) We would want to have the USARTs working anyway to support connecting the product to computers for bootloading and configuring.

So some trace cutting and more blue wires were required to the Control Head in order to get the USARTs connected. But now it should all work from the git-go with these changes applied the first prototype boards.

On Saturday, March 18, 2017 at 9:41:07 AM UTC-4, NZ0I wrote:

[NZ0I]

I posted a message to the web site describing current project status. It includes a picture of the Control Head inside the Hammond box. Take a look if you are interested: http://openardf.org

On Saturday, March 18, 2017 at 9:41:07 AM UTC-4, NZ0I wrote: