Problem using propeller backpack overlay

aznarkitekt

Hello all, I've recently purchased a propeller backpack to use in a senior design project for my undergrad studies. However, I've run into problems early on and am hoping that members of this forum can point me in the right direction. I initially encountered a problem wherein I was unable to program any part of the propeller chip except for the bootloader area, using the BPLoader. The exact problem that was experienced by this user:

http://forums.parallax.com/showthread.php?p=950516

I also did not have any luck with the older propellent version that Kevin uploaded on that thread, as it gave me the same errors still.
I downloaded the debug BPLoader from that thread and have had a bit more luck. With the prop_backpack_monitor programmed into the bootloader, I am able to program other instructions (or programs) into RAM and ROM (without overwriting the bootloader). This is still all being done with the BPLoader, however, and it is my understanding that the monitor should not be necessary unless I am programming via a Basic Stamp. I have tried to program the prop_backpack_tv_overlay_terminal, but when I put that in the bootloader, it does not allow me to program any other parts or ROM or RAM. Instead, when I try to then program the PropBP_overlay_demo, the BPLoader tells me that it recognizes the chip on port, then proceeds to try to communicate with it and then displays "No response from Backpack, or upload failed."

When I have the monitor loaded into the bootloader, I am able to program the PropBP_overlay_demo into both RAM and ROM, but I see no demo on the screen. Instead, I just see the video feed of my camera that is passed into the backpack and then out, but no overlay on it. I assume that I likely need the prop_backpack_tv_overlay_terminal programmed into the bootloader in order to run the demo (but again, this leads to my problem of not being able to program anything else when something other than the monitor is loaded into the bootloader of EEPROM).

I've also tried programming the PropBP_overlay_demo.binary straight to the bootloader and this too, simply passes my video input from my camera to my video output with no overlay on it.

Has anyone run into a similar issue? Or does anyone have any ideas on how I may troubleshoot this? I have called tech support a few times but they were unable to provide me with much feedback on the problem. I am hoping that the experience of the members on this forum will yield some sort of solution. Thanks in advance for any help or support!

Phil Pilgrim (PhiPi)

When you're attempting to upload via the bootloader, you will sometimes gt a message about pressing the Backpack's reset button to get its attention. Did you see such a message before getting, "No response from Backpack, or upload failed"? (If you don't remember seeing the reset reminder, try again, and watch for it.)

-Phil

aznarkitekt

Hi Phil, thanks for your input. I've never received any sort of message about pressing the reset button (although I've read about this in the backpack documentation). I just tried reprogramming the chip again multiple times to double check that I never received any reset warnings. Should I have prop_backpack_tv_terminal loaded into the bootloader when I try to load PropBP_overlay_demo.binary into the ROM / RAM? When I try this, this is what happens:

Searching for Propeller (on BPLoader)
Checking COM4 (on BPLoader)
Propeller chip version 1 found on COM4. (Windows Dialog Box)
No response from Backpack, or upload failed. (BPLoader)

When I program the PropBP_overlay_demo.binary straight to the bootloader, it programs, but simply takes my input video and seems to feed it right out of the output, as nothing is overlayed on it.

I am slightly confused which files should be programmed into the bootloader and which into the non bootloader sector of the eeprom. I have tried multiple configurations but still have had no luck. Is there anything else you can suggest?

Phil Pilgrim (PhiPi)

If you choose to use the bootloader (prop_backpack_monitor.binary), it must be loaded into EEPROM using the Prop Plug and the "Overwrite bootloader" setting in the Backpack Loader program. (Or you can upload it directly from the Propeller IDE.) Once there, it is possible to load a program from either the Prop Plug (with "Overwrite bootloader" UNCHECKED) or from any BASIC Stamp. Any program that will run on the Prop can be uploaded and run this way.

I've double-checked the Backpack Loader program with the latest Propellent v1.2 (2009 Aug 28), and it does work fine under Win XP. Which operating system are you using, BTW? Where is your Propellent v1.2 program located on your hard drive?
_____

As to the overlay not working, what is your video source? Some video sources do not work well with opaque overlays, causing synchronization issues with the Backpack. There's a setting you can change in the PropBP_overlay_demo.spin program to force it to use transparent overlays. Try setting TPT to 1, and see if that helps. Also, make sure both jumpers are installed on the Backpack and that you're using a good quality cable from your video source and to your monitor. Bad connections can ruin sync acquisition. And without sync, the overlay program will not attempt to overlay any text.

-Phil

Addendum: Also, for overlays, make sure you don't have video in and video out reversed. Even when reversed, you will get video pass-through, and it may even get a sporadic sync and produce some text. But your results will always be better with a proper connection.

aznarkitekt

Hi Phil, I am using the prop plug and bploader to do all my uploading. My problem is that I can not upload anything to ROM/RAM unless I have the prop_backpack_monitor.binary loaded as the bootloader. It is my understanding that I should only need to have the monitor loaded if I plan to using a BASIC Stamp to do the loading, but I am not.

I am using a 32 bit version of Windows 7 but I have tried running in every compatibility mode available as well as running as administrator. I have tried running the bploader with Propellent outside of the directory (and pointing to it) as well as inside the bploader directory and confirmed that the .ini is pointing to the correct Propellent.

My video source that I am using is a small analog wireless camera. I am plugging the camera receiver output into the input of the backpack and plugging the output of the backpack into the composite input of my lcd tv. I have checked to make sure that I do not have the input and output reversed by checking for continuity between tip with video out and sleeve with video in. I've also checked continuity between the jumpered pins for both video and overlay to make sure those are properly connected.

I will try changing the TPT and see how that goes. Thanks again for your help. Can you clarify, however, the order in which things should be loaded into the backpack if I am only using the prop plug and backpack loader to upload programs? I should just have to upload the binary into the EEPROM (with overwrite bootloader checked) correct?

Again, I greatly appreciate your help!

aznarkitekt

Hey Phil, great news! Apparently my video source was subpar for this. I plugged in a video game console instead of the wireless camera I was using and everything came right up. Now I just need to find a wireless camera that is capable of providing good enough sync signals. Would you happen to know what I need to look for in a wireless camera to know that it will work with the propeller?

Phil Pilgrim (PhiPi)

aznarkitekt wrote:

It is my understanding that I should only need to have the monitor loaded if I plan to using a BASIC Stamp to do the loading, but I am not.

That's mostly true. However, if you do not have the monitor loaded, you must always use the "Overwrite Bootloader" setting.

aznarkitekt wrote:

Apparently my video source was subpar for this.

You may yet be able to rescue your wireless camera. Most often, the problem is incorrect source impedance (i.e. too high). Try putting a 150-ohm resistor across the camera's output (i.e. before the signal gets to the Backpack), and see if that helps.

-Phil

aznarkitekt

Hey Phil, thank you very much for the clarification. I am currently experimenting with the user defined glyphs mentioned in other threads and plan to implement your "hack" on my wireless cam tomorrow to see if that helps at all.

I am also designing the portion of my PCB which will house the propeller chip and its components. I would like to replicate the video overlay section of the backpack on my PCB, as I would like to use it to create a HUD for my senior design robot. Looking at the schematic for the backpack, I have a few questions about the components and would greatly appreciate if you could provide suggestions.

1) The EEPROM in the backpack schematic is listed as 24C512. I found this part online as an ATMEL EEPROM. However, the part number listed on the chip on my backpack looks to be H726 2FB 2. Are these one and the same? Or was a different EEPROM put on the backpack and the schematic never updated?

2) Will any standard 10 MHz oscillator suffice for the XO / XI pins? I did not see any part numbers listed for that particular part so I assume something generic should work, but please do correct me if I am wrong.

3) For the video overlay portion of the circuitry, I see that 2 MOSFETs are required. Is there a certain type of MOSFET with certain specs that are required? I do not remember a whole lot about transistors but the ones on the backpack appear to be PNP?

I am mostly concerned about what MOSFETs to use as these components appear to be controlling the video overlaying. Thank you sincerely for your help!!

Phil Pilgrim (PhiPi)

1) The EEPROM in the backpack schematic is listed as 24C512. I found this part online as an ATMEL EEPROM. However, the part number listed on the chip on my backpack looks to be H726 2FB 2. Are these one and the same? Or was a different EEPROM put on the backpack and the schematic never updated?

Because of their small size, surface mount parts often have shorthand legends printed on them that seem to have no relation to their part numbers. Here's the page from the Atmel AT24C512B datasheet that explains the legend that you see:



2) Will any standard 10 MHz oscillator suffice for the XO / XI pins? I did not see any part numbers listed for that particular part so I assume something generic should work, but please do correct me if I am wrong.

The crystal used in the Backpack is an ECS-100-20-30B-DU. It's a parallel-resonant crystal with a 20pF load capacitance. If you have room on your PCB, you can also use a 5MHz crystal with the same specs otherwise. Here's a thread that discusses Propeller crystals:

http://forums.parallaxinc.com/forums/default.aspx?f=25&m=360790

3) For the video overlay portion of the circuitry, I see that 2 MOSFETs are required. Is there a certain type of MOSFET with certain specs that are required? I do not remember a whole lot about transistors but the ones on the backpack appear to be PNP?

The MOSFETs are a single-package dual nMOSFET. (The terms "NPN" and "PNP" are applied only to bipolar transistors, BTW.) The part number is a Rohm UM6K1NTN. It is characterized for gate drives as low as 2.5V. This is important. If the chosen MOSFET requires too high a gage drive, it will not switch efficiently with the Prop.

The MOSFETs are used for controlling the transparency of the overlain characters and their background.

-Phil

aznarkitekt

Phil, you've been extremely helpful! Thank you very much! I tried using a 150 Ohm resistor across the camera output as you suggested but this did not help much. Is there a way I can measure the impedance that I have to match in order to use this camera? If not, do you know what I need to look for in a wireless camera to know that it will work w/ the backpack syncs?

Phil Pilgrim (PhiPi)

Just so we're on the same page here: You said it was a "wireless camera", right? Where are you taking its output to feed to the Backpack? Where would this output normally connect if you were not using it with the Backpack? Can you provide a make and model number for the camera?

Thanks,
-Phil

aznarkitekt

Hey Phil, that's correct, it's a wireless camera. It came with a receiver base that it transmits the video feed to. I am taking the output of the receiver base and using that as the input to the backpack. In normal use of the camera (without the backpack), I would the output of the receiver base directly into the composite input on my tv. The make and model is: Swann SW231-SCK 380 TV Lines MAX Resolution Safety Camera Kit - Wireless Family Monitoring & Observation. Just a cheap camera (and this is probably the reason for my troubles ) that I bought off of newegg. I can vaguely make out what appear to be overlay glyphs scrolling quickly/diagonally across the screen, probably attributed to the sources not being synced. When I added the 150 ohm resistor across the receiver base output to lower the source impedance, it changed the video feed slightly. Now, with the resistor in place, the signal comes in and out randomly (TV displays a NO SIGNAL warning when the signal is out) and there are still small traces of overlay flying across the screen.

Phil Pilgrim (PhiPi)

Are you sure that the Backpack's video input and output are not switched? Try swapping them and see what happens. Did you try the TPT setting that I recommended?

-Phil

aznarkitekt

Hi Phil, I've verified that the input and output are not switched, according to the backpack schematic. I've also tried swapping them to see what happens and the image appears to be pretty much the same. I've also tried the TPT setting that you recommended, although come to think of it, I haven't tried changing the TPT after soldering the resistor onto the wire. Just to verify, when you said to put the 150 ohm across the camera output, you meant in parallel with the signal wire, correct? I would assume this is is correct since we are trying to lower the impedance of the source signal, but please correct me if I am wrong. Thank you!

aznarkitekt

I just tried changing the TPT to 1 and using the new hacked wire (with the 150 ohm resistor) and the image does not seem to change at all. It still appears fuzzy with diagonal static lines scrolling up and down the screen.

Phil Pilgrim (PhiPi)

Where are you located? It occurred to me that you might have a PAL camera, instead of NTSC. The camera you spec'd comes in both flavors.

-Phil

aznarkitekt

Hey Phil, I'm located in Gainesville, FL in the US. I've never used any PAL devices in my life and am quite confident that the camera I am using is NTSC. I see listed in the manual: NTSC: 510x492 / PAL: 628x582. However, I do not see any way to choose which format to use. It works perfectly with my tv at home though, so I guess it's safe to assume that the camera is operating in NTSC mode?

aznarkitekt

Hi Phil, I've got another update for ya. I went out and picked up another wireless camera, this one made by GE. I tried to overlay the video on the camera feed and it is indeed overlaying. However, the overlay flashes randomly and will not stay solid on the screen. The base receiver on this camera outputs via a 1/8" jack, so I have not had a chance to try many different cables. This is the next thing I plan to do, as you previously mentioned that cable quality may come into play. Do you know what the flashing of the overlay is indicative of? It would seem to me that the syncing is correct since the overlay is showing up where it's supposed to. Is this correct thinking? I have checked all connections to make sure they are secure, and I can not seem to find the source of the flashing.

Phil Pilgrim (PhiPi)

I have to confess I'm a bit at a loss then:

1. The camera works fine by itself with the TV.
2. Another video source works fine with the Backpack overlay program.
3. The impedance correction didn't help.

The only thing I can think of is that maybe the video signal is riding on a large DC offset. Do you have a 'scope that you can use to view the camera's output? If not, try AC coupling the camera to the Backpack using back-to-back 47uF electrolytic caps, or one 22uF non-polarized cap.

If worse comes to worse, I'll buy one of those cameras myself to test it. At $30, it's not like they cost an arm and a leg, and I really would like to get to the bottom of this.

-Phil

aznarkitekt

I scoped the video signal coming out of the first camera's base receiver. The peak to peak voltage seems to stay around 740-760 mV. I will try to get around to the AC coupling tomorrow. In the meantime, would you happen to have an idea what could cause the overlay flashing on the new camera I bought? It seems synced correctly and the cables I am using are of good quality.

Phil Pilgrim (PhiPi)

aznarkitekt wrote:

The peak to peak voltage seems to stay around 740-760 mV.

This is with a 75-ohm load, correct? If so, that's about right for a brightly-lit subject. Without any load it should be double that -- up to 2V P-P. But, if it's riding on a large DC offset, it could still cause trouble. So what DC levels did you observe on your scope?

The fact that the overlay flashes on and off with your second camera indicates an intermittent loss of sync. Can you scope that camera as well -- both AC and DC levels (with and without a 75-ohm load)?

-Phil

aznarkitekt

Hey Phil, I don't recall there being any DC offset when I scoped it. Can you clarify how the resistor should be connected to the wire to achieve the 75-ohm load? I haven't really done much hardware as I am mostly a programmer these days, and I vaguely remember studying impedance matching. I have tried a few different configurations with the resistor: in series with the signal line, in parallel with the signal line, and in between the signal and ground lines.

I will be back in the lab tomorrow evening to rescope both the old and new camera and will update you then. thanks!

Phil Pilgrim (PhiPi)

To attach a 75-ohm load to the output, just put a 75-ohm resistor from the center pin signal) to the shield (ground).

-Phil