I am making a small transmitter in the style of the Scitoys transmitter. The crystal oscillator I am using is a 1.2288 MHz that is rated at 5 volts. I am going to reverse the transformer so it will work with an MP3 player. I am a real novice: can I use the 9 volt battery that the plans call for or do I need to use 5 volts?

I would use 5 volts.

There are cheap easy-to-use regulator chips, like the 7805 that will regulate at a fixed 5V output.
http://www.ti.com/lit/ds/symlink/ua7815.pdf

Rich

4 penlights would be simpler and much more efficient than wasting power with a regulator off 9V. Yes, I know, 4 penlights isn't 5 volts either but it's closer than 9V and drop across the 1k winding DCR (70 ohms) should be about right for a typical osc 17mA draw. If using rechargeables 5 would be about right.

The question is can I use the 9 volt battery as shown? I want this to be very small so it will fit in the back of an old radio with an iPod shuffle. I plan to connect it directly to the antenna post. I am a real novice here I don't want to change the design since I would not know how. I can change the battery I use if I need to.

I blew one of my crystal oscillators. Since then I've been cautious.

You can get a battery holder that will fit your connector and holds four AA batteries, with much more life than a 9V battery. As stated above, using rechargeables will get your right at 5 volts.

Do you have a meter? Then make a voltage divider with two resistors tapped at 5 volts. It won't be as efficient
as a regulator but will work ok if you don't care about excess battery drain.

Alternatively you could try a fixed resistor in series with the oscillator, starting your trials with a high value pot. The needed value you get to
may be small enough to pass enough current for the thing to work.

If you can find out how much current the circuit draws, Ohm's Law will help you determine the value of the dropping resistor.

Or you can put a light bulb or two in series with the circuit. Look up miniature bulb specs on the web.

You can drop voltage with diodes. Diodes in series don't drop as much voltage as you'd like.
But it may be within the save limits of your oscillator.

Besides the previously stated excellent suggestions, that's all I can think of.

Actually, I meant 5 rechargeable cells for 6V.

It depends on the osc but typical current draw for the 1 MHz ECS units, for example, is 17mA and the 1k winding on the Radio Shack transformer has a reported 70 ohm DC resistance, so 17mA would drop 1.19V leaving 4.81V on the osc.

As I understand it, you want to hide this inside a radio, plug an ipod into it and clip the output directly to the radios antenna? Why not just install a jack into the radios circuit for the ipod? I suspect having a transmitter inside a playing radio will, at the least, cause oscillation problems.

Larry

Why not hide the oscillator in a small box? You could use an LM-317 variable voltage regulator to set the voltage for the oscillator and an LM-7805 along with a USB port for charging the iPod. You could then set it near the radio and use a small piece of wire for the antenna. If your radio has larger than a 6" speaker I recommend using a larger transformer otherwise the bass response may suffer due to the small transformer.

I can tell you from experience not to put to high of an audio signal through the transformer or it will burn out the oscillator chip. What I do recommend is that you use something to mix the stereo output of the iPod into a mono signal.

If your oscillator uses TTL components, you are limited to 5 Volts max. They should survive 6 V, but that's taking a small chance.

Get a data sheet for your oscillator can and review the voltage limits.

Rich

Actually, Abs Max for TTL is 7V. "Recommended Operating Conditions" is 5V, plus or minus 5% (7400 series), which goes up to 5.5V. The 74HC series has the same 7V abs max but is much more generous with 'operating', giving 2V to 6V as the range.

Unfortunately, the ECS datasheet doesn't specify technology other than to say "compatible with" nor does it give abs max numbers and Jameco, which was the source given in the Scitoys article, is even less informative about theirs.

The problem is further compounded because we're looking at DC but the transformer is going to swing both ways so you're over driving the OSC no matter what the supply. Well, that is, if you go over 40% mod with a nominal 5V on the osc and taking 7V abs max as the limit.

Note that, as previously mentioned, the transformer 1k winding has a 70 Ohm DCR so, with the ESC osc typical current draw of 17mA, a 6V battery stack will result in 4.81V nominal DC on the osc.

http://www.abracon.com/Support/qtzcryoscil_glossary.pdf

This supplier says 5.5V max. 7 V may be OK, but why do it?

It would really help to have a data sheet for the oscillator can.

Rich

I don't know if they mean operating or abs max but in any case I didn't say "do it" My suggestion was a 6V battery stack leaving 4.81V on the osc, based on the ECS typical operating current.

However, even with a rock solid 5V supply you're going to run it over 5V because you're modulating the power pin both above and below 5V.

At this point I think it's pretty much a matter of 'see if it works' because the very nature of the circuit is operating it out of spec, on both the high and low end.

In my limited torturing of these osc, they've briefly seen 10v and survived(I use a 0-25v variable P/S for B+) ...

As mentioned when connected to the high impedance side of a OPT, there is going to be voltage drop... I've seen as much as 6v so even at 12V input the osc isn't severely over voltaged... So far the best the best modulation came with 6BM8 audio output transformer using secondary for B+ and limiting voltage to approx 4v at the osc(was distorted at higher or lower settings)... I also have a 360pf cap on the output fed into a tank circuit consisting of a 150uh paralleled with a padder cap... Even so the harmonics are not completely filtered, but increased amplitude by probably 3x... While it's sort of OK, has a loooong way to go to be in the league with my tube units...

Tom

I think when I started this thread I said I was a "real novice"... every one of you went over my head. So I just built the transmitter as it was shown with a 9 volt battery I enclosed it in an Altoids Tin and attached an iPod Shuffle to the transmitter. I then set it inside one of my tombstone radios and attached the antenna lead and ground and it works very well with no oscillation problems. I played it for 6 hours straight with no problems. I do not want to add a port to the radios for an iPod since they did not come with one. I was following what was done by this guy on You Tube. "Vintage tube radio with MP3 AM-band transmitter"
http://www.youtube.com/watch?v=ryMTlhWYz3E&list=FL2EB3wjMYj2wHEFduIvUYpA&index=6&feature=plpp_video


When I attach the transmitter to a 9 foot wire antenna the volume is very low and there is a hum.

If I knew how to do this I would.

I would have to see a drawing to add in the parts. I can follow plans but that is about it.

Disclaimer: I am 15 and my Uncle John is letting me ask questions on here to learn. He said he could tell me but he wants me to find the answer if I can. He is helping me restore a Philco 630. But he wants me to do this by myself.

Congrats Johnac

You will learn by trying. Occasionally, you may zap something, but it's one way to learn.

Rich

Bravo!

Hi, I've built a few of these and they work surprisingly well with only a few parts. If you want to drop a 9V down to 6V or so, just wire 4 silicon diodes in series with the + lead. Each diode will drop about .7V so four will give about 6.2V. Simple and cheap. If you want to improve it a bit put a L-C tank on the antenna output. A variable capacitor and an old ferrite antenna rod from a junk radio work fine. The ferrite rod will actuall work as the antenna for about a meter or so.

Keep experimenting,

Doug

Here ya go, each diode drops .7v... This applies to silicon types, germanium that generally not used for such applications drop .3v...

BTW you can ignore the components in the antenna circuit(this is my version) but if you want signal to cover more than a few feet, they make a major improvement...



Tom

Tom,
Thanks for the design. I do want this to get out a bit more than a few feet so i have a couple of questions. The 150uh inductor, is that a torrid or one that looks like a resistor? If I build one like this what do I do with the ground? Just using it in the back of the radio attach the ground to the radio and it gave me clear sound. Thanks so much for all the help. Sorry if I am asking too many questions.