Costco Video Monitor for the Propeller
Phil Pilgrim (PhiPi)
Posts: 23,514
I was in Costco the other day and made an impulse purchase: a dual-screen portable DVD player ($99):
Now, not being the owner of any screaming backseat rugrats that need constant entertainment to keep quiet, why would I want one of these? What attracted me was the NTSC/PAL video input on the slave unit. I figured I could use the slave unit as a peripheral for the Propeller and still have a one-screen portable DVD player that's supposed to run five hours on its fully-charged internal LiPo battery. The master unit also has USB and SD ports, so it can possibly be used as an electronic picture frame.
Now before going any futher, I should say that this appliance has received universally bad reviews on the internet. In fact I could scarcely find a good one anywhere after I got it home. Moreover, while testing it I was not able to get the DVD player in the master unit to recognize a disk until -- in frustration -- I rapped the unit on the table while the disk was spinning. I must've dislodged some internal stiction, because I haven't had any trouble with it playing DVDs since.
The slave unit's A/V input jack accepts one of those 4-conductor 3.5mm phone plugs, except that it has to be an extra long one, as does the 4mm power connector. I don't know where you'd find either one, if you wanted to make up your own cable. Fortunately, though, it comes with a converter sporting an A/V plug that forks into three RCA jacks.
The power requirement for the slave unit states 9-12V @ 1A. I measured the current with a video input (no audio, so the speakers weren't being driven) and got 230mA, which isn't bad for a 7" LCD screen. As a consequence, the unit also runs cool.
As a Propeller peripheral, it produces a very nice, bright, wide-screen format image. (There's no way to change the apsect ratio.) But there is a caveat. The video input specs say 1V P-P at 75 ohms -- pretty standard. What they don't say is that the slave unit's input is unterminated! As a consequence, a board that uses the Parallax standard resistor array for video output (e.g. the Propeller Demo Board) produces a completely washed out image, because its output impedance is not 75 ohms. When driving an unterminated monitor, it produces a 3.3V P-P signal. I was able to get a good picture with the Demo Board, however, by strapping a 100-ohm resistor across the RCA connector. The Propeller Backpack does not have this problem, and I was able to get a good picture with a straight connection. I believe, however, that the picture might have been improved somewhat with a little additional load resistance.
Would I recommend this unit? I'm happy with mine, overall. I think it will make a nice compact peripheral for my Propeller Backpack, as well as for a modified Demo Board. But I would definitely recommend getting it from Costco, if you plan to obtain one. If you end up with a lemon, Costco's liberal return policy could save you both money and hassle.
-Phil
Now, not being the owner of any screaming backseat rugrats that need constant entertainment to keep quiet, why would I want one of these? What attracted me was the NTSC/PAL video input on the slave unit. I figured I could use the slave unit as a peripheral for the Propeller and still have a one-screen portable DVD player that's supposed to run five hours on its fully-charged internal LiPo battery. The master unit also has USB and SD ports, so it can possibly be used as an electronic picture frame.
Now before going any futher, I should say that this appliance has received universally bad reviews on the internet. In fact I could scarcely find a good one anywhere after I got it home. Moreover, while testing it I was not able to get the DVD player in the master unit to recognize a disk until -- in frustration -- I rapped the unit on the table while the disk was spinning. I must've dislodged some internal stiction, because I haven't had any trouble with it playing DVDs since.
The slave unit's A/V input jack accepts one of those 4-conductor 3.5mm phone plugs, except that it has to be an extra long one, as does the 4mm power connector. I don't know where you'd find either one, if you wanted to make up your own cable. Fortunately, though, it comes with a converter sporting an A/V plug that forks into three RCA jacks.
The power requirement for the slave unit states 9-12V @ 1A. I measured the current with a video input (no audio, so the speakers weren't being driven) and got 230mA, which isn't bad for a 7" LCD screen. As a consequence, the unit also runs cool.
As a Propeller peripheral, it produces a very nice, bright, wide-screen format image. (There's no way to change the apsect ratio.) But there is a caveat. The video input specs say 1V P-P at 75 ohms -- pretty standard. What they don't say is that the slave unit's input is unterminated! As a consequence, a board that uses the Parallax standard resistor array for video output (e.g. the Propeller Demo Board) produces a completely washed out image, because its output impedance is not 75 ohms. When driving an unterminated monitor, it produces a 3.3V P-P signal. I was able to get a good picture with the Demo Board, however, by strapping a 100-ohm resistor across the RCA connector. The Propeller Backpack does not have this problem, and I was able to get a good picture with a straight connection. I believe, however, that the picture might have been improved somewhat with a little additional load resistance.
Would I recommend this unit? I'm happy with mine, overall. I think it will make a nice compact peripheral for my Propeller Backpack, as well as for a modified Demo Board. But I would definitely recommend getting it from Costco, if you plan to obtain one. If you end up with a lemon, Costco's liberal return policy could save you both money and hassle.
-Phil
244 x 174 - 22K
Comments
You can get used 15" VGA LCD's on ebay for $10.00 up + shipping all day long.
Jim
Oh bummer. I'm glad you pointed that out to me.
I guess ebay it is.
Thanks!
AV cables can be bought from eBay. There are basically two connection variants - iPod and Video Camera/Nokia phone. The tip and next ring are standard stereo, but the last 2 rings vary from GND TV or TV GND. This requires a cross-link on the prop. (see the wiki)
PS I am using the 4pin 3.5mm connector on an upcoming project.
I'd be surprised if this were true. An LCD screen is basically a digital device, so it would make no sense to convert the DVD signal to analog NTSC first and then back to digital for the signal kept within the master enclosure. But I could be wrong.
On this connector, ground is the outer ring, video, the tip, and audio the two inner rings. But electrical compatibility is the lesser issue. The real problem is mechanical compatibility. Because of the case thickness, both the power and A/V connectors are extra long. Here's a photo that compares them (the inner two) with "standard" connectors having the same number of circuits:
I've tried the standard connectors and they don't work because they don't insert far enough. But for my app this doesn't trouble me because I've got the A/V adapter, an extension cord that connects the two units, a wall transformer with the correct plug, and a car cigarette lighter adapter, which can all be scavenged.
Thats an unusual AV connection from what I have seen.