Hello,I am new to this forum and very new to electronics.I am trying to learn as much as I can,but I am the type that only after I actually complete a task will I understand it completely.I bought an LM380 kit to build an easy intercom circuit(It says great for a kid or beginner,so I really feel like a moron).The Schematic shows a simple transformer symbol as T1=25:1.The part that is confusing me is the kit does not come with a transformer.The only thing I can figure is I could use one of the potentiometers,which the kit did come with.I know this is probably a simple question to answer,but I have searched the web for two days and can't get a clear answer of whether or not a potentiometer would work or what the difference between a step down transformer and a pot is.Any advice would be helpful.I attached the schematic for this circuit.Thanks in advance.INTERCOM 2(a).jpg
Attachments
It came with 2 Pushbutton, SPST Momentary,switches.It came with many capacitors,resistors,pots,4 transistors.The kit is for a variety of circuits,but I wanted to do the simple intercom first.At least I thought it was going to be simple.Like I said I am very new to circuits.
The kit should have come with a transformer unless they have changed it. the 25:1 transformer is there to act as a step-up transformer to allow the speaker to be used as a microphone.
It's a real pity these circuits and kits are so hit and miss especially for a beginner.
That transformer is crucial to the design as Jaycee points out...
Have you got a link to the kit so we can have a look 🙂
You ask the difference between a pot and transformer.... well the short answer is they are two totally different things.
The pot allows you to "tap" of a voltage along the length of its carbon track using the middle terminal or "wiper. It can never increase the signal level.
The transformer can provide a voltage gain... in your case from the tiny voltage the speaker produces as a microphone into something larger that the LM380 can work with... but you don't get something for nothing doing that, but that's another story.
That transformer is crucial to the design as Jaycee points out...
Have you got a link to the kit so we can have a look 🙂
You ask the difference between a pot and transformer.... well the short answer is they are two totally different things.
The pot allows you to "tap" of a voltage along the length of its carbon track using the middle terminal or "wiper. It can never increase the signal level.
The transformer can provide a voltage gain... in your case from the tiny voltage the speaker produces as a microphone into something larger that the LM380 can work with... but you don't get something for nothing doing that, but that's another story.
Here is the link to the kit and parts.NightFire Electronic Kits : (#1415) LM380 2.5 Watt Audio Power Amplifier Kit - $8.25 don't know why my last post did not show up,so if this gets posted twice I am sorry.Thanks for the info. so far.I don't feel quite as stupid knowing that I am supposed to have a transformer to complete this.If anyone knows of a link to a simple circuit I can build with these components,I would greatly appreciate it.If not I have seen other schematics of this same intercom except they use a transformer from Radio Shack #273-1380.If I have to I will order this part and complete the Intercom with it and the other components from the kit I bought.
This is not a kit as such, just a collection of components which includes a LM380.
No circuit diagrams are supplied with it and there appear to be no recommended projects for it only suggestions. It is up to the buyer to decide on a circuit and obtain those parts which are not supplied.
No circuit diagrams are supplied with it and there appear to be no recommended projects for it only suggestions. It is up to the buyer to decide on a circuit and obtain those parts which are not supplied.
Sorry for not replying earlier...
First off it's worth having the data sheets for parts handy, and for ic's these often give applications too... I see where your circuit came from now,
http://www.datasheetcatalog.org/datasheet/nationalsemiconductor/DS006977.PDF
Data sheets from
LM380 Datasheet pdf - Audio Power Amplifier - National Semiconductor
It might be worth experimenting... if you can get an old scrap ancient transistor radio, the old 6 transistor types of 40 years ago lol, these had small trannys in them for matching the speaker to the amp... probably just right for your project.
First off it's worth having the data sheets for parts handy, and for ic's these often give applications too... I see where your circuit came from now,
http://www.datasheetcatalog.org/datasheet/nationalsemiconductor/DS006977.PDF
Data sheets from
LM380 Datasheet pdf - Audio Power Amplifier - National Semiconductor
It might be worth experimenting... if you can get an old scrap ancient transistor radio, the old 6 transistor types of 40 years ago lol, these had small trannys in them for matching the speaker to the amp... probably just right for your project.
The parts did come with schematics and the Intercom was one of them there is a pdf on their website that shows the projects that can be made with the LM380.I don't have a problem ordering a transformer,but it is very confusing to a beginner to be given a bunch of parts and schematics and then not have the right parts for the schematics sent.I am sure there are a dozen circuits that can be built with these components,as I said I have about ten different schematics sent with the parts,but the only one that interested me was the intercom.I am going to order the Transformer used in the other schematics for this circuit which steps 8 ohms up to 1kohm.I am determined to build this now.I have seen other more advanced schematics that show an Intercom system without Transformers built with the LM380,but they take many more components and I am just trying to get one circuit to work and then I can understand more about how circuits work than if I read 10 manuals,that is how my brain works.Once the circuit is done I will understand the opamp's and other components purposes much better.Thanks for all the help and advice.It has saved me many days of searching the internet.
I just thought about a rheostat device I bought that was made to decrease the wattage of a heat lamp with a turn dial.It would adjust a 100 watt heat lamp down to off.Obviously it had to have some type of transformer in it.It quit working after about a week.If I can remember where I put it I am going to take it apart and see if maybe there is something useful in there.Does anybody have any knowledge about rheostat devices and if they would have a transformer I could use?Everyone has been so helpful so far and I value any advice you may have to give.I have always been interested in electronics and I want to learn as much as possible,so maybe a year or two from now I can help answer these questions instead of asking them.
Thanks for the advice Mooly.Somehow I missed your reply before I last posted.The links you have posted to the LM380 has one of the pages that was sent with the parts,page 3 was sent with the 4 projects along with another sheet.The 2nd sheet said it required the purchase of another part to complete those tasks for a few simple alarms,but the first sheet(page 3 of the pdf LM380) said nothing about additional parts.That is why I assumed everything I needed was in there,but I assumed wrong.I am going to look around for some things I can take apart and try and find something that may suffice before I order the transformer.
A lamp dimmer will probably be an an electronic device using a thyristor/triac to control the power. Like the speed controller on a power drill 🙂
If you really want to learn you can't beat a plug board (breadboard) and a box of bits and just have a go making all sorts of stuff... there's no quick way to learn... but if you are really interested you will find it all comes easily.
Why not have a go at a simple amplifier or headphone amp etc
If you really want to learn you can't beat a plug board (breadboard) and a box of bits and just have a go making all sorts of stuff... there's no quick way to learn... but if you are really interested you will find it all comes easily.
Why not have a go at a simple amplifier or headphone amp etc
I just got a few more pcb's in the mail so I think I am going to just find the simplest diagram I can find and make something,whether it works or not.I have been trying to be careful only having that one board that came with the kit,but now I can at least use some of those resistors and capacitors to better my soldering skills if nothing else and like you said Mooly there's no quick way to learn,but I think the best way is actually trying to make stuff in my case anyway.I can read about ohms law until I'm blue in the face,but I'm not going to understand it until I see it in action.Thanks again for all the advice.I will let you know how things work out or don't work out either way!
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