556 IC Output to CK108 FM transmitter

[vortex00]

I'm working on a project to have it transmit a tone
which is applied to the line input(RCA jack) of the CK108 unit(canakit.com). I
am using a 556 IC. Using Pin 9(output) of the 556
chip works fine with a speaker thru a 100uF cap.

What components should I use on the output from pin 9
of the 556 IC to get a signal into the 108 unit similiar to the output from a walkman, cd player, etc. which it's setup to receive.

Thanks,
Jack

 

[audioguru]

The CK108 has a low level microphone input. Its spec's don't mention a line level input.
Whatever the input, your 556 oscillator needs a two resistors voltage divider to reduce its output voltage to the amount needed.

 

[vortex00]

Thanks working on the values. Should I be measuring AC or DC from the 556 IC?

 

[audioguru]

The 556 has a tone output which is AC. Its frequency is too high for a multimeter to measure its amplitude accurately. A multimeter is made to measure 50Hz or 60Hz mains frequency. An oscilloscope can measure it.

 

[vortex00]

OK, I made a 10:1 voltage divider to drop the voltage for the line input to the FM transmitter using a 10K and a 1K resister.
It still doesn't work unless I leave the speaker in the circuit and then it starts to oscillate where before I had a steady tone but it least it transmits marginally. I'm sure it changes the charactoristics but I'm at a loss of the next step to further refine. Any help?

Thanks,
Jack

 

[audioguru]

If the 556 and transmitter have the same battery then it needs a few hundred uF supply bypass capacitor.
The voltage divider has a DC output near 0VDC. Therefore it must be capacitor coupled to the input of the transmitter.

 

[vortex00]

Seperate power supplies. 9V for the 556 and 6V for the FM Tx. Gommon ground though.
I'll work on capacitors from Pin 9 to the line input along with the voltage divider.
I already have a 10uf prior to the speaker.

Jack

 

[Hero999]

Could you please post the schematic.

 

[vortex00]

Here's the schematics for the IC556 tone generator project. Objective is a steady tone when pin 5 is not connected, intermittant when pin 5 to pos 3(IC pin 10),warble pin 5 to pos 1.

I want to remove the speaker and connect pin 9 directly to the line input of the FM Tx.

I've connected a 10:1 (10k to 1K) voltage divider but it only marginally works with the speaker still connected. With the speaker removed, very poor to inop.

Different power sources used.

Just trying to match the output to the line input.

I appreciate any help.

Jack

 

[audioguru]

The 556 is way overloaded with the speaker as its load. Maybe your 9V battery is also overloaded and reduces the output level. The output of the 556 is way higher than line level.
Your 556 circuit needs a 100uF supply bypass capacitor.

Even a 10:1 attenuator is not enough to reduce the 7Vp-p from the 556 down to mic level (20mVp-p). Try 470k, 1M or 4.7M instead of the 100k.

 

[vortex00]

...your 556 circuit needs a 100uF supply bypass capacitor-

Not sure what this means. Put the cap across the 9V battery in the circuit?
Tried it to no avail.

Replaced the 100k resister with a 1M one. near inop.

Works good with the speaker. When I attempt to change things I loose my desired result: ie. a steady tone when pin 5 is not connected, intermittant when pin 5 to pos 3(IC pin 10), warble pin 5 to pos 1.

I know I'm missing something .

Can the speaker load be substituted with a resister?

I haven't tried running it on a lower(6V) voltage.

Thanks for the help,

Jack

 

[audioguru]

The max allowed ouput current from a 556 is 200mA. With a 9V supply a 556 will have an output of about 7Vp-p. since you have a coupling capacitor to a speaker then the peak current in an 8 ohm speaker will try to be 3.5V/8= 438mA. So the 556 is way overloaded and will get too hot. You are lucky that it still works.

 

[vortex00]

OK, got it. good info. probably never even got hot because I just test it at 1-2 sec intervals.

I'll try working with it w/o the speaker and just use the earbuds from Pin 9.

What would you do to solve the problem?

Jack

 

[audioguru]

Connect a resistor in series with the speaker to reduce the current. Even earbuds could be 8 ohms and cause overload so add a resistor in series with them also.
The output level of the 556 will hardly change when loaded with 200mA peak and no load, then you can adjust the attenuator to work properly.

 

[Hero999]

Using earbuds could/will deafen you!

 

[habibullahkhan]

hi Sir,

hello Sir,, I m a technical teacher in pakistan and teaching electronics radio in here .I have many tubes (ECH81,,EF89,,EBC81,,EF89,EL84,,EZ80,,).I want to build an FM radio transmitter having frequency 100MHz and range two kilometer,If u have any circuit diagram about this ,please send me circuit diagram and guidance by my email ,i m very thankful to u , my email is
khu313@gmail.com
if u have any am transmitter circuit diagram for tubes mentioned above send me please too
thanks,,
Habibullah khan

 

[Nigel Goodwin]

hello Sir,, I m a technical teacher in pakistan and teaching electronics radio in here .I have many tubes (ECH81,,EF89,,EBC81,,EF89,EL84,,EZ80,,).I want to build an FM radio transmitter having frequency 100MHz and range two kilometer,If u have any circuit diagram about this ,please send me circuit diagram and guidance by my email ,i m very thankful to u , my email is
khu313@gmail.com
if u have any am transmitter circuit diagram for tubes mentioned above send me please too
thanks,,
Habibullah khan

Those are a set of valves for an old valve radio RECEIVER - there's nothing there suitable for making a VHF transmitter.

 

[audioguru]

Tubes are good for heating a room in winter.
Transistors make a little radio transmitter.

I think you are about 55 years too late.