SparkFun Forums

[adamthole]

I've been experimenting with the 315mHz RF-KLP and have a few questions.

First, one of the places I have been testing is a rather noisy grocery store (CRT's, various refrigerators, etc.) I am picking up a good amount of interference and haven't been able to get much of a range, yet. I was curious if I was using the 433.92 Mhz would the interference be any lower? Is their any advantage to any of the frequencies?

It says to make an antennae out of wire. Does it matter what kind of wire? Stranded, solid? What is the best home-made antenna?

My goal here is to get rid of the dead spots and increase my range.

Thanks!

[Pete-O]

The noise in your space...hard to say. The frequencies in question require no license (lisence?), so anybody and their brother could be on them. As for other noise sources, they could be an issue if your antenna is close to them, but I expect the harmonics off a CRT to taper off after a few MHz and a fridge or freezer lower than that.

There's no particular advantage of 315 or 433 over the other that I can think of. Although, multipath effects could be in play (good chance), and 315 might be better because of the longer wavelength.

A wire antenna should be fine. Type of wire isn't a big deal, though a purist might say to use stranded. The length will be critical. Make sure that's correct.

Good luck

Pete

[adamthole]

Okay, with the antenna I have an increased range. However, I am having another problem now.

Now that the full circuit is hooked up, it works intermittently. When I press a button on the transmitter, the receiver powers a transistor, which powers an electric DC motor. When that motor comes on, it takes alot of the power from the receiver and then goes off shortly. My guess is that the motor is drawing too much current and the range of the receiver is greatly decreased. (It stays on if the transmitter is right on the receiver antenna). This causes the motor to turn on and off, in a neat way. This feature is actually desired in one of my projects, however in the other it is not.

I am currently using a supply of 3 C cells, wired up in series (approx 4.5 volts). Is their any way to get rid of this intermittency, without adding another power source? My goal is to run it all from the 3 C cells, but it isn't looking like that will be possible.

Also, on my other design, by letting it be intermittent, am I hurting anything?

Thanks.

[Pete-O]

I'd be surprised if the 3 C's couldn't source enough for you. But DC motors are notorious noise makers. I would suggest putting some electrical distance between your RF and that motor. Decouple the bejezuz outa that thing and see if it gets better.

Letting it be intermittent shouldn't be a problem. But remember that if it's doing something that you didn't tell it to do, we still define that as "problem". Or you could do like Microchip does and call it an "undocumented feature".

Pete

[adamthole]

Thanks Pete-O. It isn't noise. If I use a seperate battery for the DC motor it works with no problems. So I don't know what it is.

I'm having anyother problem though. Why won't the receiver work ith anything but batteries? When I hook it up via a 5V wall adapter, it doesn't work/gets 2 inches of range. With 5V batteries, it does great. Am I missing something, or doing something wrong?

[Pete-O]

Why won't the receiver work ith anything but batteries? When I hook it up via a 5V wall adapter, it doesn't work/gets 2 inches of range. With 5V batteries, it does great. Am I missing something, or doing something wrong?

OK, that one is definitely noise. Wall warts are noisey devices, batteries are quiet. You could try better decoupling to use the wall wart, maybe use some polystyrene caps and get them as close to the power pins as you can.

[sparky]

Check the voltage on your 5V Wall wart. My bet is that is says 6-7V. 5V is the rating when loaded at the rated current. Unloaded, you'll have much higher voltage.

Pete's right, you need a regulator, caps, etc. Wall warts are just good current sources - bad voltage sources.

-Nathan

[adamthole]

Yeah, it puts out like 6V I believe. When I hooked it up to the KLP I used a resistor, so I didn't go over the maximum rating.

I'm still new to the electronics industry, so sorry if this is a dumb question. When you say caps, you mean capacitors, correct?

Anybody know of any simple schematics of a circuit that will convert my wall wart into a nice 5V source?

Any more ideas on the intermittency? of the motor? Would some voltage regulator help out their also perhaps?

Thanks!

[sparky]

Yep caps = capacitors. Don't worry, I didn't know what polarized electrolytics where either when I started . Start reading on google. Search for things like

pic tutorial circuit schematic

5v power supply pic example

etc.

-Nathan

[adamthole]

Okay, I've been doing some research, and I think I've found out how to make a 5V regulated source. I need a voltage regulator, and approximately 15 V or so going into that with a combination of capacitors. That is cool, and will help me out on one of my applications.

However, one of my applications requires that both my receiver and my DC motor to be ran off of approximately 4.8V, from one source. Is their anyway I can make a more regulated source from my batteries, without adding more voltage? I don't have any more room in my enclosure for more batteries. I searched google with no luck. Thanks!

[Pete-O]

I probably wouldn't drive a 5V regulator with 15 volts in because it's gonna get HOT. Your regulator will have to dissipate twice as much power as your load. Try something like 4 dry cells (4X1.5=6V). In order for the regulator to work right you've got to have some overhead, but not usually that much. A 7805 regulator will work at about 6V in, last time I checked. And in my world, approximately 4.8V is approximately 5V. You should be good to go at that point.

Maybe we should just make a good 5V regulator board and sell that...

Pete

[geekything]

Why not use a switching or PFM regulator?

-marc

[adamthole]

I have had some free time latley and I finally got the HT12D and HT12E to work together. I find it very interesting how much differently the HT12D works than the a5885m worked (the chip I used previously).

In the a5885m, when the chip was not getting the proper input, all of the outputs would go inactive. However the HT12D will keep all outputs at their current state if it does not receive an input from the receiver. This means that if the output is active and the user goes out of range, that output will stay high until the user comes back into range and the transmitter tells it to go low.

This creates a problem and solves a problem for me. I no longer have the intermittency problem, however the motor doesn't turn off. I have to unhook the motor for it to turn off now.

Any suggestions on how I could either 1.) make it intermittent again or 2.) make it function properly? Thanks.