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Recent Questions

September/October 2018


Scoping Out Some Advise

Certain techs and engineers still have a need to sample and view composite/NTSC video in its three axes form, that is: X axis (horizontal), Y axis (vertical), and Z axis (intensity).

In the past, this was accomplished using a CRT o’scope: horiz sweep to H input; vert sweep to V input; and video to Z, or intensity modulation input. Since CRT scopes are bulky, heavy, and, in most cases, not battery powered, a PC/digital scope with capture capability would be very handy for field use.

None of the scope ads I’ve seen list these features. Can anyone make some recommendations?

#9181
Paul Dendrenos
Barstow, CA


Resonator Frequency

I have in my junkbox what I believe to be ceramic resonators. What is the best way to test them to determine their frequency?

#9182
Donald Frazier
Geneva, IL


Something Strange With The Range

The effective range of the key FOB for my Ford F150 seems to have decreased over recent months. While it used to work from distances of 75-100 yards easy, now I need to be nearly right in front (10-20 yards) of my vehicle to operate the systems. I changed to a fresh battery, but no difference. Is it likely there is an antenna problem? If so, where is it located and is there a test procedure?

#9183
Les Waldroup
Charlotte, NC


Wireless Data To PC

I have a number of wireless temperature/humidity sensors made by Oregon Scientific for use as weather station sensors. I would like to use them for a data acquisition and monitoring application. Does anyone know what frequency and mode they operate on and how I might use them to send data to a PC to record seasonal trends? Would I need a microcontroller to interpret the output or could it be read directly by the PC and then logged and displayed using software such as MakerPlot?

#9184
Jai Hooley
Edmonton, AB


July/August 2018


Smooth LEDs?

What makes some LED replacement bulbs dimmable, while others are not? Some of the replacements I have purchased do not dim very smoothly. They seem to dim in steps and then just turn off before lowering to where I need them to be. The previous incandesants dimmed much more smoothly down to a soft glow. Is there a different, (maybe more expensive) type/technology that  would more closely emulate the incandesants? I'm using an X10 controller for the dimming, could this be the problem?

#7181
Everett Barham
Elvaston, IL



Answers

There is no such thing as a dimmable LED. The way we get around this is by using Pulse Width Modulation (PWM), which means the LED is turned on for shorter and shorter periods of time within a time frame. You can see that if the LED is turned on for 100% of the time, say 1/100th of a second, then it is on for 10,000 1/10,000ths of a second, the LED will be only 1/100th as "bright" if it is turned down to being on only 1/10,000th of a second for every 1/100th of a second.

I used 1/100th of a second as the time frame because the human eye can't see flickering when the flicker rate is around 1/50th of a second, this is why old analog TV's in the US used 1/60th of a second to build a picture frame, and in Europe they used 1/50th of a second for their TVs.

You can also think about this using a 1 second time frame if you want. In this case when the LED is on only 1/100th of a second for every second of time frame it would appear only 1/100th as bright. The problem here is that we would see the LED turning on and off, so we would lose the appearance of the LED dimming. We have to use a time frame that the human eye can't "see" such as a time frame of 0.01 (1/100th) seconds.
 

Phil Karras, KE3FL
via email

A LED is a beautiful dimmable device; lower the current, and the output brightness goes down. This can be done through simple resistors, or through PWM (Pulse Width Modulation). That is the good news.

In order to use a LED as a house incandescent lamp replacement, something needs to be done to make that possible. First of all, the voltage is WAY to high, it is AC (the LED prefers DC), and we need to feed it the correct current. So a power supply module is included to convert the 120 (or 220) Volt AC to some small DC current appropriate for the LED used.

Herein lies the problem. This PS module is designed to deliver x mA to the LED more or less regardless of the input. When you adjust the input, the PS module tries to compensate, to the point where it no longer can, often resulting in a flickering light. These are the now non-dimmable LED bulbs.

To make this “house” LED bulb dimmable, a radically different PS module must be built. It must sense that the input has changed (due to the dimmer setting), and adjust the LED current accordingly. Not easy to do! and of course, more expensive.

Several designs have been marketed, some better than others. In most cases, even with a “dimmable” LED bulb, a special dimmer is required. It is a mess, and most still don’t work perfectly.

Bill van Dijk
Carp, Ontario

I can’t answer specifically what is different about dimmable LED lamps, but will note that the type of dimmer is important. You need to use a dimmer specifically designed for LED lamps.

I have had good luck with Lutron CL line of dimmers that are made specifically for LED lamps. These are not X10, I have not seen any X10 dimmers for LED lamps. Also note that X10 light controls generally only work for incandescent lamps, they need a bit of current flowing through the filament to work correctly.

For LED lamps I have used the relay based X10 switch WS13A with good success, it also works with CFLs.

Dan Koellen AI6XG
Roseville

Different bulbs behave differently so you have try some options. There are some test results on the X10 Forum that you might find useful. X10 dimmers dim in 16 levels so some bulbs may not dim smoothly.

Bruce Robin
Naples


TV Image Capture

What’s the best way to capture images from my TV? I’m looking to do something like a computer “print screen.”

#7182
Sharon Fitzgerald
Chattanooga, TN



Answers

There are two “inexpensive” ways to do a print screen from a TV screen:

1. Put a digital camera on a tripod and set it up in front of the screen — ensure the TV screen fills the viewfinder and ensure the flash is off. When you want to capture something, just take a picture of the screen.

After that, connect the camera to your PC via USB cable and download the screen capture. Be aware: the resolution of the photographed image will be limited by the screen resolution of the TV screen AND don’t be surprised if you get screen bars, etc. due to the timing between your camera’s shutter and the TV’s screen image refresh.

2. Install a stand-alone DVD recorder between your cable box and TV, or connect the recorder to your TV’s video out jack using a suitable interface cable. What you’ll do is record the program to the DVD (use DVD-R discs) and use the machine to finalize the recorded DVD (make it playable on other DVD drives) when the recording is complete.

Then, play that DVD on your computer’s DVD drive, use the computer’s playback program (i.e., Media Player for Windows) to get to the screen to capture, then PAUSE the playback. Use the image capture feature of the player to take a snapshot of the video image, then save it to your disc.  Be aware: the resolution of the DVD-recorded material will be no better than the video signal (Composite, S-video, HDMI) fed to the recorder.

After you’ve screen captured your images to your computer, use your Image Editing utility to clean up, etc. the images for your use.

Now then, there’s a more expensive way to do it: it involves installing a video capture card into your PC. Like the DVD recorder option, you’ll have to patch the video signal from the cable box or TV’s Video Out into your video capture card.

This way, you can watch TV using your PC and, using the Video Capture Application Software, capture a snapshot in (more or less) real time. Also, you can record the program, while you’re watching it, to your PC and edit/manipulate the recorded material at your leisure.

The big advantage is your captured images will (typically) be the screen resolution of your computer’s display (or at least much better than the inexpensive options above).

Ken SImmons
Auburn, WA

This would be most easily accomplished using an HDMI splitter and an HDMI-capture device used with your computer.

HDMI-capture devices can be external (to the computer) for PC or Apple machines, or can be implemented as a pluggable card for use with a PC desktop machine (assuming that the machine has an unassigned motherboard PCIe connector available).

Connect the splitter to the television program source – e.g., a cable box. Using an HDMI cable, connect one of the splitter outputs to the television set. Using a second HDMI cable, connect the remaining splitter output to the HDMI-capture device.

Record the program material using the software provided with the HDMI-capture device. See Newegg et al for available devices.

Peter A. Goodwin
Rockport, MA


Phone Line Intercom

We use our cell phones as our main phone service, so our “land line” is no longer being used. Is there a way to use the house phone wiring along with the old phones as a whole house intercom system? I have a detached garage/workshop away from the house where this would be especially useful, not to mention almost every room is wired. Would I need to disconnect from the phone company "grid" to do this?

#7183
Jay Bousquet
Lexington, NC


Show Me The Power

When renovating houses as a hobby, I need to locate powerlines inside the walls and also underground. What curcuit can I build that would be useful? Also, what is the theory of how such a detector would work?

#7184
Denzel Meier
Winnsboro, SC


PCBs With PTHs

Is there a hobbyist method for making circuit boards with plated through holes at home? Also curious by what is meant by multilayer boards. I'm just getting started, so forgive if this is an obvious newbie question.

#7185
Leonelo Márquez
Maplewood, MN


May/June 2018


PS2 Emulation

My Sony CD changer has a PS2 keyboard port to enter the CD title, details, etc. Instead of typing, is there a way to emulate a PS2 interface on a PC or processor board to automate the key presses?

#5181
Lee
Schaumburg



Answers

I have successfully plugged an old PC keyboard into that CD changer to enter data. However, what is it that you want to automate? Every entry i.e. artist, titles, etc.; are different?

M. Herman
LaQ, CA

Yes, you can emulate a PS-2 keyboard. An SPI-master port will do the job as long as it can handle 11 bits, or two 8-bit values in rapid succession. Not all microcontrollers can. (If you lack a good SPI port, emulate it in software.) Use the MOSI signal for the key-code transmissions and use the SCLK signal to emulate the keyboard’s clock output. The bits transmitted when you press a key look much like those put out by a standard UART: a start bit, eight data bits, an odd-parity bit, and a stop bit.

The keyboard’s clock output produces a logic-1 in its idle state and created a positive edge for each of the 11 bits. An SPI port configured as CPOL=1, CPHA=1, provides the proper timing. Note: The least-significant bit of an 8-bit key value gets sent first. My old PS-2 keyboard produces clock signals at 13.7 kHz. That’s a good frequency to start with for the SPI port.

A PS-2 keyboard assigns a unique non-ASCII code to every key. Find a list of the keys and assigned codes here: https://techdocs.altium.com/display/FPGA/PS2+Keyboard+Scan+Codes. When you press the “A” key, for example, the keyboard’s circuit produces the hex code 1C. When you release the “A” key, the keyboard transmits a key-release code F0, followed by the key’s code again.

The shift key works the same way. To send an uppercase “A” your microcontroller or processor board would send the SHIFT-key code, the A key code (then a short delay) followed by the key release code and the A key code again. Then it would send the key release code followed by the shift-key code.

Remember, your code must calculate an odd-parity bit and insert it in the 11-bit value to send. You can find parity-generator code on the Internet. Also, ensure you send the key and release values in bit-reversed form. Thus, the 1C code (0001 1100) for “A” must get transmitted as 0011 1000. You can simply set up your code so it uses the “reverse-bit” values to start with.

Jon Titus
Herriman, UT


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