# How to read digital LCR meter

#### audioguru

##### Well-Known Member
It is against the law to use the FM transmitter because it causes interference if it is tuned to a radio station frequency. The FM transmitters used in cars to have an RF attenuator to reduce their range to within the car. Mine can be received on a good car radio across a river valley 2km away.

Learn about how transistors work to see what reducing a 9V supply down to the 4V to 6.4V from four AA batteries. Three AA batteries drop to 3V when many circuits will not work.

I do not know the technology of a "gum drop" cap. A film capacitor is good for audio, a ceramic capacitor is good for RF.

#### gary350

##### Well-Known Member
This is the other circuit I found online almost identical to the circuit I listed but this one has several extra parts and different transistors. Data sheets both look about the same.

#### audioguru

##### Well-Known Member
Your 2N2222A FM transmitter circuit has the value of R1 much too low which reduces the output level from the mic. Then capacitor C3 parallel with the emitter resistor R9 of the audio transistor Q1 provides way too much voltage gain so its output is clipping and very distorted. Then R7 attenuates the distorted audio and feeds R5 and R8 that have values much too low.
The value of C4 is much too high (mine is 200 times less) and cuts all medium and higher audio frequencies and again important pre-emphasis is missing.

I noticed that the "Engrish" on the circuitspedia website is as bad as the circuit errors. Guess its country.

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#### Nigel Goodwin

##### Super Moderator
I was wondering if stray capacitance would be a problem in this circuit.
I mentioned that in post #8, layout of these crude transmitters is crucial. and as AG posted a proven working layout that would be a good place to start.

It's not unusual for such circuits to not work at all, wrong frequency, drift all over the place, be heavily distorted etc. If you're making a PCB then you might have to try a few before you hit on a 'good' one.

#### gary350

##### Well-Known Member
Your 2N2222A FM transmitter circuit has the value of R1 much too low which reduces the output level from the mic. Then capacitor C3 parallel with the emitter resistor R9 of the audio transistor Q1 provides way too much voltage gain so its output is clipping and very distorted. Then R7 attenuates the distorted audio and feeds R5 and R8 that have values much too low.
The value of C4 is much too high (mine is 200 times less) and cuts all medium and higher audio frequencies and again important pre-emphasis is missing.

I noticed that the "Engrish" on the circuitspedia website is as bad as the circuit errors. Guess its country.
I knew that 2N2222 circuit was screwed up that is why i was going to built the 2N3904 circuit. I am going to build your circuit but at the moment I can not build it with C13 I can add that on later after I buy more variable capacitors. If I order caps today maybe they arrive quick maybe 1 week. I have built online circuits before Nigel is right they often don't work at all. I have a book called. Malcoms 101 electronic projects, the book name needs to be changed to, Malcoms 101 electronic projects that don't work. LOL. I did manage to get several of those projects to work and made changes in my book. Online circuits are the same way many don't works, if they do work they don't work right.

WHAT is that circuit board you built your circuit on, I have never seen those how do they work?

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#### audioguru

##### Well-Known Member
C6 and C13 are tiny variable capacitors that I bought at a local electronic parts store. Most of my parts were ordered online from Digikey or Newark in my neighbouring country United States (I am in Canada). If I order before 8:00 in the evening then my order is delivered to my home the next morning.

Stripboard is a perforated circuit board with parallel strips of copper on it. I attach photos that explain how it is used.

In my job I made thousands of custom circuits that only one or two were needed. The prototype was made on stripboard and sometimes a part or two needed to be changed which was easy with my solder-sucker. The end result worked perfectly and looked so good that it was sold as the finished product.
Some of the circuits were very complicated and the circuit board was large. There is software online (stripboardmajic. stripboardcad etc) that helps design the parts layout but I liked using my brain instead.

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#### gary350

##### Well-Known Member
I ordered 4.7pf capacitors $3 for 100 they will be here about Wed from Colorado. Variable capacitors are$10 to $20 each unless I order from china$1.60 for 100 but it will take 2 to 4 weeks. I dug deeper into my part found another 5 - 85pf variable cap. C6 is 5-45pf. C13 is 5-85pf. I have moved parts around on the PC board 3 times finally got them almost how I want them. I have 40 more of these PC boards I will use a different PC board to solder parts to 1 by 1. This PC board is a temporary holder. All the wires will be on top, resistor wires fit in same holes as transistors & capacitors. Bottom side will have several solder spots where 2 or 3 wires are in the same hole. I don't like these PC boards very much I would rather have the other kind with copper traces in rows. C13 & L2 need to be moved 1 holes to the left. I had all the parts except the 4.7pf. I bought 20 caps 5-45pf for $1.61 free postage they be here in a month. I wonder if the 5V regulator will need a heat sink. I never did find my package of new Electret Mics, oh well I ordered more$1.81 for 30 free postage. This might be tricky to adjust 2 variable capacitors to the same Hz.

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#### audioguru

##### Well-Known Member
Your voltage regulator looks huge and high current, what is its part number? I used a smaller lower current low dropout regulator since it still regulates when the 9V battery voltage has dropped to 5.5V. An ordinary 7805 voltage regulator drops out and fails when the 9V battery is still fairly new at 7V or less.

I do not see the important ceramic capacitors C2, C5, C9, C10, C12 and C14 in my circuit on your circuit.

C6 tunes the radio frequency and C13 is tunes for the maximum signal strength (farthest range).
High quality Western variable capacitors are much less expensive at Digikey than what you found. Here is a link:

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#### gary350

##### Well-Known Member
I need to look see if i have a LM3931A I used 7805 because I had 1 laying right in front of me. Yes I better look for an ML3931

Well poop, I forgot C2. LOL.

C7 is not there it will be here next week maybe Wed. All the caps are there pf caps are tiny ceramic almost same color as PC board. C14 is south of the L2. C12 is left of Q3.

Looks like I made a mistake on C9 & C10 I used 1000uf instead of 1000pf I need to change that. Looking at my notes I wrote down pf instead of uf. WOW first mistake I ever make. LOL. If you believer that you believer anything. LOL

I will fix it tomorrow.

#### gary350

##### Well-Known Member
I can not find LM3931A anywhere. Google keeps showing me LM393 other places do too.

I am going to use 6 AA batteries. 9V batteries go dead too quick.

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#### jjw

##### Member
I can not find LM3931A anywhere. Google keeps showing me LM393 other places do too.

I am going to use 6 AA batteries. 9V batteries go dead too quick.
It is LM2931A

#### gary350

I don't have any LM2931A voltage regulators. I can buy 1 they are not cheap with postage about $10. I have four LM317 variable voltage regulators it needs 7 parts to make it work, 2 variable resistors that I have, to dial in 5v. It has variable current regulator too 10ma to 1.5a. http://www.ee.teihal.gr/labs/electronics/web/downloads/LM317T_Variable_Voltage_Regulator.pdf It looks like I can power Q1 and Q2 with 4.5V from 3 AA batteries. Another 4.5V from 3 AA batteries = 9V on Q3. Last edited: #### JonSea ##### Well-Known Member Most Helpful Member I don't have any LM2931A voltage regulators. I can buy 1 they are not cheap with postage about$10.
I've said this at least once in this thread, but I will try once more. Even if Gary ignores me again, somebody may benefit.

Arrow has the LM2931A in a number of varieties. One of them, in a TO92 package, is 64 cents. Since the US has to claim Gary as one of its citizens, overnight shipping from Arrow is FREE.

Arrow doesn't have the stock of Digikey, but it's growing. The price is generally less than Digikey or Mouser, and overnight shipping is free. Arrow also accepts PayPal, for very low hassle ordering.

#### audioguru

##### Well-Known Member
Ten Dollars for a low dropout regulator that sells for only 63 cents? RIPOFF!

Why not look at the datasheet of the LM317 regulators that you have? When set for a 5V output they do not regulate when the battery voltage drops below about 7V and a 9V battery quickly drops to 6V. A 5V low dropout regulator works perfectly when the input drops to 5.5V.

If you use a voltage lower than 5V then resistor values must be re-calculated and replaced.

#### gary350

##### Well-Known Member
I've said this at least once in this thread, but I will try once more. Even if Gary ignores me again, somebody may benefit.

Arrow has the LM2931A in a number of varieties. One of them, in a TO92 package, is 64 cents. Since the US has to claim Gary as one of its citizens, overnight shipping from Arrow is FREE.

Arrow doesn't have the stock of Digikey, but it's growing. The price is generally less than Digikey or Mouser, and overnight shipping is free. Arrow also accepts PayPal, for very low hassle ordering.

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Search for Arrow Electronics comes up with this. http://www.ee.teihal.gr/labs/electronics/web/downloads/LM317T_Variable_Voltage_Regulator.pdf

This place has dozens of these, surface mount, transistor type body, mosfet type body, and many different variations of LM2931.

I see LM2931AZ, LM2931AD, don't see LM2931A? There are several pages says stuff different prices. Information seems to be about the same?

Information about quantity and price. One is build quantity only, one says tape reals, one says 12 week delivery, I click on
Manufacturer ON Semiconductor
.66 cents each immediate delivery, Comes up with date sheet, add to cart, next page is blank it wants to know the part number and quaitity so I type it in, next it wants to know Customer Reference:

What is Customer Reference:

I come to a dead end. No option for me to type my name and address.

I click check out again now it wants me to register.

14 minutes later finally I am at the end price is $10.55 for 1 part and no option to change it to 10 parts. #### gary350 ##### Well-Known Member I did google search for Arrow nothing? I did search for Arrow electronics found it. I do search for LM3931 order page comes up. 5 parts$3.17 free postage. Had to create an account. 20 minutes later is says, 5 parts are coming from China 16 weeks delivery.

Ebay is quicker than this.

Different part numberLM2931ZD is the transistor TO-92 case 50 parts $8. Postage from NC$2.60 be here in 4 days.

All the parts are on the PC board except for the 4.7pf cap. I will use 8AA batteries = 12V. 7805 regulator will have to work until parts arrive.

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#### JonSea

##### Well-Known Member
ARROW.COM

Sorry I didn't spell it out for you completely. I didn't think it would be that difficult.

#### audioguru

##### Well-Known Member
Gary, you get your letters and numbers mixed up. You were looking for a low dropout regulator with the wrong part number. Now you are talking about a 4.7ph inductor instead of the required 4.7pF ceramic capacitor.

Sigh

#### JonSea

##### Well-Known Member
The suffix after the part number specifies the package the part it in (e.g., T0220, TO92, SOIC-8). The data sheet is your friend.

Searching for LM2931 on Octopart.com shows some of the different options - see first picture below.

Clicking on one of the TO92 versions available at Arrow brings up the price breakdown for this part and a BUY button. See the second picture below.

Clicking the BUY button brings up the screen where you can actually purchase the part. Enter the quantity you'd like to order, and click the BUY button. Note that the screen says Overnight shipping is free. If you click any other option when checking out, shipping will not be free.

Once the desired parts are in your cart, click the cart and select check out.

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