FM transmitter (mod4)

[wakeke]

I don't have a credit account or the ones that can be used for online etc., etc. so I use most of the available resources around. I'm in the Phil. but my location is far from the capital city. Our electronic shops here doesn't have all of the common ics which are abundant compared to key cities but they manage to have similar ics (but diff. part nos.) made from the neighboring Asian (China,Korea) countries. That's why I ask & confirm ics good for substitute to lessen cost because ordering & shipping from the capital is not cheap at all & even more costly if getting from outside the country.

I was able to know some other LDO regulators (datasheet sites) similar to LM2931 & will try to look for them in the local shops. But if these aren't available & the ordinary volt. regulator is not suitable, I will order from a known shop in the capital. Thanks if you can help about the shop and all but I can manage on that part if I can't get what I need locally.

Also, sorry for not being able to mention my location (I thought at first it wouldn't be of much help) and thanks and I appreciate you looking at the other side of the coin.

 

[circuitnoob]

Sorry I could not reply for a long time.......had exams..
I finished making the transmitter .....it works fine, but only for about 1m.
Well I replaced 160K with 180K and 30pf with 33pf but all other components are the same....what might be the problem???
I will post a pic......
**broken link removed**

 

[Hero999]

The regulation of a uA7805 is guaranteed only when its input is 8V and more. The regulation is spec'd to be much worse when the input is only 7V.

µA7805 data sheet

At 7V with voltage is only going to change by 250mV which is hardly going to cause it to drift a lot.

The specification on the datasheet is with a load current of 1A over the full temperature range, at lighter loads and room temperature, it will be considerably better.

The Texas Instruments datasheet doesn't specify the drop-out at lower currents but National Semiconductors' does.
**broken link removed**

Look at the graph on page 6.

How much current does you circuit use?

An educated guess about 50mA without analysing it in great detail.

At 0A it's 1.5V, at 500mA it's just under 1.75V.

At 50mA it'll be somewhere in between the two.

Interpolating between the two figures gives 1.525V.

The above specifications are at 0°C, at room temperature it'll be a little better.

These are typical figures, if you want the worst case then normalise the figures to those given by worst case specification, like I showed you before.

 

[transistor495]

circuitnoob,

If you are using 2N3904, then I think the transistor is connected reversely( I assume from pic)

Can't understand the first L, which is the oscillator inductor?

We can all play football over the remaining space. What you think? If you got to work on a fairly large circuit I think a 1m scale like structure is good for the pcb. Plan the component placement by your own way according to the pcb in hand keeping the instructions in mind. Cut the pcb in a miniature style before start. Planning is important.

 

[circuitnoob]

No I used BC546 instead of 2N3904.Well it works, but only for about 1m.....so does the length of my circuit has something to do with the range of the transmitter??

 

[transistor495]

Why can't use the specified 2n3904 itself? Its commonly available everywhere. BC546's power handling is low.

*) Layout and placement is bad.
*) Power amp stage and coupling is bad.
*) Inductors are bad. Why you didn't follow the inductor design of the original design?
*) It doesn't look like an fm transmitter

You've to change the layout to a miniature design and rebuild the inductors to make it alive on the fm band. Even my single AAA cell transmitter covers an area of 50m without any RF amp!

 

[audioguru]

There are excellent electronic websites in The Philippines (but not in Philidelphia).
Most of the people there know what is available in the markets there.

 

[audioguru]

The spec's for the BC546 are nearly the same as the 2N3904 so it should work the same.

Maybe you connected its C and E pins backwards since they are like a mirror of the 2N3904.

 

[circuitnoob]

transistor495
Well 2N3904 ain't that much easy to obtain at Sri Lanka..so they gave me BC546. The inductor on the left was taken by a sony radio, and its definitely 0.1uh but the other one i made by hand using calculations. i made it more compact before but ended up with lead areas joining together .......Well if the components are fixed incorrectly it would not work ryt?? My guess is the inductor i made by hand is wrong ...so i will change it

 

[whiz115]

An ordinary voltage regulator IC does not oscillate when it has the input and output capacitors shown in its datasheet.

how do you explain the oscillation problems i was facing since i was doing exactly what the datasheet said.. my TI regulators wasn't "ordinary" ?

I have never seen the texas Instruments low dropout regulator.
they show it with no output capacitor, 1uF and 10uF. They do not show what happens with a 100uF output capacitor. Try a 1uF output capacitor.

i did it...and the sound pitch gets higher than it is with the 100uF
i have also connected the NR pin with a 10nF capacitor to the ground.

Audioguru i'm thinking to cut the rail at some point before the regulator and add there the murata ferrite bead that i told you on an older post... do you agree?

you don't need an inductor in series with the regulator.Instead you need a low dropout regulator that does not oscillate.

transistor495
Well 2N3904 ain't that much easy to obtain at Sri Lanka..so they gave me BC546. The inductor on the left was taken by a sony radio, and its definitely 0.1uh but the other one i made by hand using calculations. i made it more compact before but ended up with lead areas joining together .......Well if the components are fixed incorrectly it would not work ryt?? My guess is the inductor i made by hand is wrong ...so i will change it

try using axial inductors (the ones that look like a resistor...) i don't know about high Q and low Q... the point is it works if you get the right value.

also the second LC tank i believe it isn't so much important.. Audioguru helped me remove it.

 

[circuitnoob]

try using axial inductors (the ones that look like a resistor...) i don't know about high Q and low Q... the point is it works if you get the right value.

also the second LC tank i believe it isn't so much important.. Audioguru helped me remove it./QUOTE]
Well i first tried using them.....but its hard to obtain inductors with low values such as 0.1uh

 

[whiz115]

Well i first tried using them.....but its hard to obtain inductors with low values such as 0.1uh

i got every part from local shops at my city.. also some inductors between 100nH and 180nH.

if it is hard for you to find then stick with the recomended way and use air coils.

 

[transistor495]

Art of Electronics

Your second inductor look nice but hold it tightly so that it won't fall down from the edge

Why can't you try the original inductor as it is. Around 9turns on 3mm air core I think. But you've made the supply regulator in between the oscillator and output amp that is bad and affects the coupling too. AG has well done!

I treat electronics as an art. So bad layout design is not in my dictionary(lol..). Few years before my brother caught me calling my assembly 'spider net' and gifted a breadboard as well. Need not to say I'm very thankful and it boosted my experiments a lot

 

[audioguru]

I kept other parts away from my LC tuned circuits. I spaced my air coils up away from the circuit board.

 

[circuitnoob]

I made the circuit again...i reduced the length from about 3inches. This time i followed this circuit so i could plug my mp4 player to it. It works fine, I still tested it to about 10m ...but there is a "treeeeeeeeee" sound that goes along with the sound (well the sound is kind of very clear). What is the reason for this?? **broken link removed**
**broken link removed**

 

[Hero999]

Try:

• Retuning the transmitter and radio to find a less noisy frequency.
• Using screened cable for the audio, co-axial cable will do.
• Putting the transmitter in a screened enclosure, with a hole for the aerial obviously.

Your layout doesn't look very good; what signals are those yellow wires carrying? They could be adding lots of inductance and capacitance and pick up all kinds of EMF.

 

[thecoolsundar]

bldc Design from scratch

Hi,

could someone guide me through the steps of how I would go about designing a bldc motor, knowing only the following requirements;

a) Power 300W
b) voltage 24V
c) Torque 40 Nm
d) RPM 180
e) Max external dia = 254mm
f) Max length = 90 mm

So now I need to know;
1) How many poles do I need? and why?
2) How many teeth? and why?
3) How many windings? and why?
4) Of what diameter wire? and why?
5) What dimension magnets? and why?

Would much appreciate if you can get me started.
I'm sure I can take it from there
Thanks

Sunil

 

[Hero999]

No, please start your own thread rather than rudely interupting someone else's.

 

[thecoolsundar]

i cant

i can't find the new thread button

 

[Hero999]

It looks like this: