Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

can you have a look at my eagle board layout - the Guru's mic amp

Status
Not open for further replies.

danrogers

Member
basically this will be the first board ive designed other than simple led arrays etc.

could you take a look at how im doing so far and suggest improvement and more importantly re-assure me that it will work :)

thanks
 

Attachments

  • psu and mic amp..png
    psu and mic amp..png
    38.2 KB · Views: 524
  • psu and mic amp s&.png
    psu and mic amp s&.png
    41.8 KB · Views: 336
Last edited:
Please post a schematic as well as the PCB layout.
 
There doesn't appear to be anything wring with the PCB layout.

However I don't know about the schematic because you've drawn the op-amp as a box rather than using the proper symbol.

The box is meaningless and it means you need to keep refering to the datasheet, in order for the schematic to make sense. If you use the real op-amp symbol then the schematic will make sense, without having to look at the datasheet and it will be easier to read too.
**broken link removed**
 
thats a very good point. I guess ive kind of merged a schematic and a layout diagram and it should obviously be 100% schematic!

thanks for checking :)

is there anything you would suggest to make the board layout look more professional and/or efficient?


edit.. there we go :)
 

Attachments

  • psu and mic amp s&.png
    psu and mic amp s&.png
    15 KB · Views: 322
Last edited:
That's better.

A couple of the capacitors were connected backwards.

C3 was polarised when it should be a non-polarised film capacitor, not ceramic.

I'd also consider making C6 non-polarised or replacing it with a 1µF electrolytic capacitor.
 

Attachments

  • mic pre-amp..png
    mic pre-amp..png
    9.4 KB · Views: 366
Last edited:
ah yes thanks! I didnt notice that, slightly different symbols.

I guess non- polarised means that electrons can flow from pole to more easier or something?

thanks for the help mate
 
You are missing the 47uf capacitor to ground at the junction of the 1k and 10k resistors.

A 78L08 won't work from a 9V battery that drops to 6V. It needs a minimum input of 10V.
The circuit does not need a voltage regulator.

If the output connects to a shielded cable then a 100 ohm series resistor at the output must be used to isolate the capacitance of the cable to avoid oscillation.
 

Attachments

  • Electret mic prea.PNG
    Electret mic prea.PNG
    5.1 KB · Views: 282
Hi Guru,

So in other words i can scrap the regulator and just power from a 9v battery?

Thanks for pointing out the missed cap, I dont know how I missed that.

I have yet to work out the output stage, Im not sure if you remember but I want to use the output to activate a transistor to act as a switch for a RF encoder input. - Thats the next challenge to overcome :)
 
Hi Guru,

So in other words i can scrap the regulator and just power from a 9v battery?
Yes because the regulator's input voltage is too low for it to regulate and all it will do is make the supply to the opamp about 7V without regulation when the battery is new and less when the battery runs down.
The 100uf capacitor filters the battery voltage pretty well.
 
I see that makes sense now thanks.

Back to the output stage I've been thinking again (although im not sure what kind of voltage/current the amp will put out).
In your opinion what i be best off using a transistor to act as the switch, a phototransistor, or a coil to activate a reed switch?
 
I have never used a reed switch so I don't know the current in the coil.
If it is 100mA or less then a transistor can easily drive it and the base current of the transistor is 10mA or less which most opamps can drive.
You need to limit the base current to the transistor and maybe add a diode so it does not become too negative.
The relay coil needs a reversed diode across it to arrest voltage spikes.
 
I guess non- polarised means that electrons can flow from pole to more easier or something?
Non-polarised capacitors tend to be used more <1µF and for 100nF there's often no choice but to use a non-polarised capacitor because 100nF electrolytic capacitors are rare and probably more expensive.

Film capacitors should also be used wherever possible because they have lower distortion than ceramic or electrolytic capacitrors.
 
You need to limit the base current to the transistor and maybe add a diode so it does not become too negative.
The relay coil needs a reversed diode across it to arrest voltage spikes.

would current limiting be ok with a resistor? I guess i would'nt need a diode unless using a coil then? Cheers Guru


And thanks Hero for explaining that about capacitors, great help :)
 
I have never used a reed switch so I don't know the current in the coil.
If it is 100mA or less then a transistor can easily drive it and the base current of the transistor is 10mA or less which most opamps can drive.
You need to limit the base current to the transistor and maybe add a diode so it does not become too negative.
The relay coil needs a reversed diode across it to arrest voltage spikes.

Could you suggest a transistor with those traits? I'm not really clued up on them to be honest!

thanks
 
Each reed relay has spec's.
Each transistor has spec's.
Simply put them together.
 
You must match the transistor to your reed relay.
You selected a tiny darlington transistor that is only 3mm long. Maybe you cannot connect to its tiny pins.
It is a darlington type that has a fairly high voltage loss.
 
Last edited:
I thought a reed rely would be an option without using a transistor or a transistor as a second option?

Should be ok with that size package as I will probably etch a board and Im ok with soldering smd

but as you say thats a tiny transistor and probably 'underkill' for my application!

I've just been reading up on some types of transistors. would a BJT type best suit or something else?
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top