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Two PCBs off of one power source


CALAHAN
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These are regular alkalines by the way. I will be using AAA lithiums in the final version because I need to bring the amperage somewhat back up as I replaced the 3 AA for these 3 AAA's. I wonder what effect those will have.

AAA cells will produce exactly the same current to your circuit as AA cells except they are smaller and won't last as long.
Lithium keeps the voltage higher, longer than alkaline.

I have a pristine FRS model of the one I hacked for the communicator, so I used this for the breadboard. I did exactly as you indicated. I took one of those "earbuds" and put into the headphone jack, cut the earpiece end of it off, stripped the wires, ran one to ground and the other to the breadboard as indicated and found that there is no sound coming through the speaker (I used a second FRS and created sound to be able to hear of course). I can hear the other FRS through the earpiece (I have two of those also), but the spliced one is not amplifying through the chip. Other then that, all is working.

One wire from the earbuds is the signal and the other wire (pin 3 of its power amplifier) has a DC voltage that must not be connected to ground. Maybe your wires were mixed up. I showed the DC wire with a cut, then the earbud's wire was connected to ground.
If you connected pin 3 of the FRS power amplifier to ground then maybe the IC is blown up.
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Audioguru,

I can't solder wires to parts of the FRS circuit board. That would be very risky, even if I could find those locations you pointed out on it. As for the earbud, I plugged it into the headphone jack, the other end was stripped and I put alligator clips on the ends to the breadboard.  You mean to tell me that if I cross those two wires I stripped, the whole thing is blown?  I was under the assumption that one wire from the earbud was hot and the other ground. Is this not correct? there is nothing touching that one contact coming off the positive battery terminal in that jack array. I didn't do anything to the FRS circuit board. In fact, I took an unaltered earbud and snapped it in, and the sound does come through, so I doubt anything on the FRS is fried.

I will solder jump wires off the earbud stripped wires rather then use alligator clips and try that. The ear bud is very small, and the wires a mere few strands. I'll do this to ensure proper connection. It is either the connection or the breadboard.

Is there anyway of turning the volume down a bit with this chip?  As I had stated, I really didn't need the exra volume, and it is at near distortion at this point.

Bruce

Bruce

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Hi Bruce,
Since an earbud still works then the power amplifier IC in the FRS radio is not blown.

One earphone wire has signal and the other earphone wire is not grounded and should not be grounded because it has a DC voltage. You need to connect the signal wire to the capacitor input of the MC34119 power amplifier and cut the DC wire from the earphones plug and not use it. The MC34119 can get its input ground connection through the battery negative terminal.

The value of one resistor determines the volume of the MC34119 power amplifier:

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Audioguru,

After looking at youir schematic again, I kind of figured you would say that. The MC34119 only needs the one wire out of the FRS, where I had both - one to the capacitor and the other to ground.

I'll reduce that resister also in my trials tonight. Can 1/4 watt resistors work? I need the smaller size to conserve space.

Bruce

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Audioguru,

Well my friend, it worked.

I am very pleased. After I knew it would work, I started eliminating some of those pieces to see what could be done away with without changing the sound ( I need space). I was able to eliminate the two grounds completely off pins 2 and 3. And - I was able to eliminate the 100 uf capacitor to ground off of pin 5 altogether. No change in sound quality.


Here is one issue I am having. I reduced the resistor as you stated, which did in fact lower the volume to keep the sound effects from distortion, however, it also lowers the FRS peak volume too, and I need the FRS volume.

As I had stated earlier, the sound effects chip really actually uses 3 volts, but I have been running it on the 4.5 volts and it has not fried. It is even louder as I wanted. With the amp IC added, it is too loud now and distorts the speaker. I took a 69 ohm resistor and placed it between the power of the sound effects and the positive power rail. It reduced the volume to where I wanted it and cleaned up the distortion, however, there is a constant click present. I tried to add different values of resistor, and as I increased the value, the clicking stopped, but the volume also became low and unstable. Any ideas here?


Thanks,

Bruce 

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Well my friend, it worked.

Good.

I was able to eliminate the 100 uf capacitor to ground off of pin 5 altogether. No change in sound quality.

All battery-powered electronic circuits should have a supply bypass capacitor to keep a fairly stable supply voltage as the battery internal resistance increases as it runs down. The MC34119 amplifier might oscillate without a bypass capacitor when the battery gets a little used.


Here is one issue I am having. I reduced the resistor as you stated, which did in fact lower the volume to keep the sound effects from distortion, however, it also lowers the FRS peak volume too, and I need the FRS volume.

Of course. The negative feedback resistor controls the gain of the amplifier.
Increase the value of the input resistor to decrease the volume of that input. 

As I had stated earlier, the sound effects chip really actually uses 3 volts, but I have been running it on the 4.5 volts and it has not fried. It is even louder as I wanted. With the amp IC added, it is too loud now and distorts the speaker. I took a 69 ohm resistor and placed it between the power of the sound effects and the positive power rail. It reduced the volume to where I wanted it and cleaned up the distortion, however, there is a constant click present. I tried to add different values of resistor, and as I increased the value, the clicking stopped, but the volume also became low and unstable. Any ideas here?

A supply bypass capacitor across the IC would probably help but you don't have space for it. Try using two small diodes in series instead of the resistor. The diodes will reduce the voltage about 1.4V and will have a very low impedance.
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Audioguru,

I shoudl use those small black colored silicone diodes witht he white band from Radioshack? Out of curiosity, which was does the band face in the circuit?

And - for the heck of it, what does the supply bypass capacitor look like? Are you talking about returning the 10uf capacitor back?  The issues with that is the cylinder capacitor. If I could find a cermaic dick capacitor instead, I could find room for that.

Bruce 

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I shoud use those small black colored silicone diodes with the white band from Radioshack? Out of curiosity, which was does the band face in the circuit?

Silicone is a flexible synthetic rubber. Transistors and diodes are made from very hard silicon.
Diodes have part numbers. RadioShack is not in Canada anymore and I can't remember which ones they sold. Use two 1N914 or 1N4148 small diodes in a glass case or use two 1N400x larger rectifier diodes in a black epoxy case.

The line on a diode is its cathode. Connect the positive terminal of the battery to the anode end of one diode and connect its cathode to the anode end of the second diode. Connect the cathode end of the second diode to the positive supply input of your sound effects circuit.

what does the supply bypass capacitor look like?

It is a capacitor across the supply in every battery-powered circuit. Your sound effects circuit has a 100uF supply bypass capacitor. Your FRS radio has a few of them. My MC34119 power amplifier circuit has a 100uF supply bypass capacitor but it will work if it is only 10uF.

Are you talking about returning the 10uf capacitor back?

What 10uF capacitor?
What is "returning back"?

The issues with that is the cylinder capacitor. If I could find a cermaic dick capacitor instead, I could find room for that.

I have never seen a ceramic dick. Hee, hee.
The biggest ceramic disc capacitor I have ever seen was 1uF but schematics on the internet have 22uF ones.
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Audioguru,

I don't know how to turn on the "reply with quote" function with this message board.

When I stated returning to the 10uf capacitor, I was refering to the fact that I have removed this from your schematic to save space and there was no noticable sound difference. Now that you state that is is needed for when the battieres start to die down, I will return it.  I'm sure someone out there sells a flat ceramic disk 10uf capacitor, but I wonder how big the thing is. The little 10uf culinder is not that bad, so I'll find the room.  I take it there is no issues with me removing the ground connections of of pins 2 and 3?  When I used them my sound was messed up with or without the capacitors.

 

Tonight I will just try and change the input resistor for the sound effects end to try and turn the volume down so it won't distort. If that does not work with the resistors I have on hand here, I will use the diodes. I do think I have a few of the glass Zener diodes here. 

I also have a few 1N4001 Micro 1A Diodes

Here is the RadioShack page on them:

http://www.radioshack.com/product/index.jsp?productId=2036268&cp=&sr=1&origkw=diode&kw=diode&parentPage=search

I have the 1N4003 also which I think is the same as the 4001 but just can handle more input voltage.

I have two IN4733A Zeners also.

Bruce 

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Hi Bruce,
My MC34119 circuit uses a 100uF supply bypass capacitor but it will work with 10uF.
I have some very small 10uF electrolytic capacitors that I removed from old electronic things.
One wire of electrolytic capacitors is marked "-". It must not be connected with backwards polarity in a circuit.

The MC34119 should have a capacitor from pin 2 to ground and another capacitor from pin 3 to ground. It won't work if you grounded the pins. It might work without the capacitors.

The diodes I recommended are in the same small glass case as some zener diodes but they are not zener diodes. Use zener diodes if you want.

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Audioguru,

I'll look through some of the junk in garage for a capacitor that is smaller at 10uf, but will use the one I have if needed. There is not an issue with it working, it's just too big.

As for pins 2 and 3, I tried them with capacitors, and with direct connections to gound. Either way, the sound was heavily effected. When removing them altogether, the sound was fine with no connection to the pins at all.

Since I have the zeners here, I'll use them - if needed. The different resistor will be tried first.

Bruce 

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Audioguru,

Something happened last night to the breadboard setup. It worked initially, but as soon as I connected the FRS, and tried to change resistor values out, the thing quit working. I put the multi-tester on the power input wire for the IC chip and it showed good, but putting the probe on the actual no. 6 IC contact showed no power. Something must have been grounding.  Also, I tried direct grounding pins 2 and 3, and all it gave me was reduced volume. Puttingin the 1.0 uf resisters caused the thing to squeel. I changed the whole assembly to different holes in the board, and it worked, however, it seems that I needed to use the two diodes to control the distortion of the sound effects circuit. I also experienced the clicking I was speaking about earlier which occures if the sound effects is hooked up to the breadboard and the FRS goes into power saving mode. The only way to get rid of it was to put in the two 1. capacitors, and this time the squeeling did not happen, and the whole circuit now works what appears to be perfectly.

Something went wrong on the breadboard and I do not know what.  Tonight I will attempt to solder the amplifier circuit together for actual use in the communicator. I will advise by the end of the weekend it this was a success. It looks as though there willbe no skimping on the different components after all.

If this works, I will build one of these for all of my future FRS communicator projects, unless of course I can find room for two seperate speakers. I will always need to power both on one power supply.

Are you any good with antennas?

Bruce

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I never use a breadboard. The connections are always intermittent. I quickly sketch a parts layout then solder the parts and a few jumper wires (that do not cross) on stripboard.

Pin 2 and pin 3 of an MC34119 amplifier must never be grounded. They are supposed to have a filter capacitor to ground.

All i know about antennas is to use a quarter-wave whip or a half-wave dipole.

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Audioguru,

I inserted the new amplifier into the communicator tonight. All works great. I tweaked the resistors a bit to mix the volume levels as I wanted and no issues. Thank you for you time and patience on this - and thank you for helping me realize this childhood dream of having an actual "working" Star Trek communicator. Now I have one and will be making more. I'll be the talk of the campground.


Bruce

P.S. now to tweak the antenna a bit more. I picked up a helical 2.5" duck stubby tuned to my frequency range, and now to figure out how to hack this thing to fit in my shells and create a proper ground plane. But I have had a bit of experience in this already.

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Audioguru,

Now that am using this amp circuit, I have lost my volume pot on the FRS. I get all, or nothing.  The wipe of the resistance has been cut to immediate if you know what I mean. As I had stated early on, this FRS uses a resistor pot with thumb wheel. Any fixes?

I am also wondering how this problem will lay out when I use the circuit on an FRS with digital volume control instead of analog.

Bruce

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I changed out the main 3.3k resistor at pin 4 to 5 to get a bit more volume on the whole unit per your suggestions prior. Could this be the issue?

Please attach the schematic of what "changed out" means.
Before you said the volume was too high and you would reduce the value of the 3.3k resistor between pins 4 and 5 to reduce the volume. I don't know what value you tried and I don't know what value you have now.
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The 10k resistor between pins 4 and 5 of the MV34119 has colour bands brown, black then orange. Then the circuit has a signal gain of 7.
Maybe you used a 100k resistor instead which makes a signal gain of 61. A 100k resistor has colour bands brown, black then yellow. Then the volume control would act like an on-off switch.

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Audioguru,

This is the issue I saw coming. Remember one of my initial posts on this subject? I saw a red flag but I thought it was just my musings of a novice. Perhaps I may be right on this one.

The FRS volume is, for lack of a better term, "double cut". The original volume pot controls the audio signal  at line level (I assume), and when the volume is all the way up, the pot is letting through probably what .3 volts? (for full line level), and when reducing the volume by turning the thumbwheel,  that voltage is reduced to even less (and there isn't much to reduce). Since I have tapped off the headphone jack, instead of the speaker - am I correct in assuming that I have effectively bypassed the on board audio amplifier?

With an unamplified line level out of the FRS, "cut again" by the 3.3k resistor in the new circuit we created, I will only get volume when the FRS pot is at full volume allowing the full signal to pass, because any less then full volume is such a small amount of signal, it is inaudible.

Is this summation correct?  and if so, do I really need the 3.3k resistor on the FRS end of the new amplifier circuit, since the original onboard volume pot is already supplying line level?  I measured the volume pot some time back and I think it is 10k rated already.

Bruce 

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