# What does inverted triangle in this schematic mean?

I'm trying to make this circuit but I'm unable to understand what the inverted triangle is and how to connect them all together.

Here is the schematic, what does the inverted triangle represent?

And how can I build this circuit, can I use wires to solder to the capacitors, diodes and resistors? Will it reduce it's effectiveness?

I have Capacitors with 102pF, 103pF and 104pF, among the ones I have, which are suitable for this circuit?

I was asked to connect a thin copper wire of 12 inches as antenna, I'm planning on soldering one such wire to one 103pF capacitor and other end of this capacitor to 1n34a diode(D1) and other end of the D1 to another capacitor(C2), and another end of 103pF capacitor to 1n34a diode(D2) and this one's end to D1, below the C2, between both wires of C2, I'll solder 10k resistor, and to these ends I'll solder wires which I can insert in multimeter.

Am I doing this right? Will adding wires reduce it's effectiveness?

• – AJN
Jul 21, 2020 at 3:10
• SE policy is to split up unrelated questions into different questions. How can I build..., which are suitable..., can be split into new separate questions.
– AJN
Jul 21, 2020 at 3:13
• Those capacitors shown on the schematic as 0.001uF = 1nF = 1000pF. They often are marked 102 (10 and 2 zeros). A capacitor marked 103 is 10x more capacitance (0.01uF, 10nf, 10,000pF). Jul 21, 2020 at 3:13
• You can also describe what this circuit is supposed to do as well as the frequency ranges of operation and signal amplitudes. Extra info is required to answer "How can i build this circuit".
– AJN
Jul 21, 2020 at 3:15
• earth ground, as opposed to logical or chassis. Jul 21, 2020 at 4:53

1. This circuit is intended to pick up radio signals. Radio signals don't do well on solderless breadboards. There is capacitance between rows on the breadboard that will tend to "absorb" your radio signals. I'd solder the circuit together.
2. The circuit is intended to pick up radio signals. Radio signals don't do well with long wires. Long wires act like inductors that will tend to block your radio signals. The leads on the parts are long enough. Solder the circuit together with the shortest connections you can make. You should be able to make everything with just 1 cm long leads.
3. The "inverted triangle" is normally "signal ground" in a circuit. In a radio receiver, it should really be "earth ground" - that is, it should be connected to a long wire driven into the dirt of the earth. Since you will want this thing to be portable, it should be enough if you make the ground wire something you can touch when you carry the device. Hold the device, touch the ground wire, wave the device around looking for strong signals.
4. The capacitors in the schematic diagram are 1 nanofarad. If you are using ceramic capacitors, they will be marked "102" That's 10 times 100 (two zeros) picofarads = 1000 picofarads = 1 nanofarad.

You can build the circuit on a piece of perfboard, or you can build it by just soldering the components together.

• The diodes may be rather sensitive to heat when soldering. Clip an alligator clip to the leads of the diodes (right up by the body of the diode) while soldering to keep the heat away from the diode. Too much heat can damage a diode. It might look OK, but not work.
• Small ceramic capacitors are rather fragile. Be careful when bending the leads of the capacitors - hold the leads with a needle nosed pliers right up by the body of the capacitor while bending the leads of the capacitors. That way, the pliers take the mechanical force of the bend rather than the body of the capacitor.

I wouldn't make any bets on the frequency range of the radio signals you can receive, or the sensitivity of the device.

• It'll probably react to quite weak sources at low frequencies and short distances. (Microprocessors and a interference from other electronic devices.)
• It'll probably react to much higher frequencies but at higher signal levels at short distances. A portable two way radio (walkie talkie) will probably cause a strong reaction.
• It might react to cellphone signals (the phone transmitting) at short distance, and maybe WiFi or Bluetooth. It will depend on the length if the connections in the circuit, and how well the diodes work at very high frequencies. Try it. Might work, might not.
• Is there a way to check if diode has been damaged, I've soldered the diodes on a different project and hoping to repurpose them in this project, I want to know if they are working or not before soldering in this one. Jul 21, 2020 at 7:47
• Use the "diode test" function of a multimeter. For the germanium diodes specified, you should measure around 0.3V in one direction, and open circuit in the other.
– JRE
Jul 21, 2020 at 7:51
• When I used the diode test, I'm numbers in 8000 range, does it mean it is damaged? Jul 22, 2020 at 6:27
• The diode test function normally reads in volts. A germanium diode should read around 0.3V. If you are getting different numbers, check the manual for your meter and make sure you are using it correctly. It may also have a chart or description showing how to understand the readings.
– JRE
Jul 22, 2020 at 10:35

I'm just getting started myself, but I think the inverted triangle (the one at the bottom?) is Signal Ground (not power ground). But what you connect this to I'm not sure. I've read about using a metal cold water pipe in your building, or a long metal rod driven into the actual ground.

I'm not sure about the rest, sorry. However, be careful not to overheat the diodes. Apparently it's a good idea to use alligator clips or the like as a heatsink to protect them when you solder.

Good luck!

• Do the diodes get damaged when they overheat? I need to know what I have to connect to the inverted triangle. Jul 21, 2020 at 5:19
• The inverted triangle can be considered to be common; i.e, you don't have to do anything special. Just connect together all the wires that are shown to be connected to common. As mentioned in another answer, this common point can also be connected to earth if you want.
– AJN
Jul 21, 2020 at 5:51

The inverted triangle symbol represents 'signal ground'.

A signal ground serves as a return path for signals and power and also serves as a common reference for incoming and outgoing signals.

In the circuit being referred, it is the common terminating point for D1, C2 and the 10kΩ resistor.

The components may be soldered, 'point-to-point' on a perforated board, using short leads. A PCB may also be used.

Capacitor values are marked on them using the 3-digit value code. For a capacitor marked '102', the first significant digit is '1', the second significant digit '0' and the number of zeroes that follow '2'. The value of a capacitor marked '102' would be 1000pF or 0.001μF.

The two 0.001μF capacitors, you are to use, would be marked '102'.

• Thanks for this help. Can I do this on breadboard too? What kind of copper wire do I have to use for antenna? How can I make a common terminating point for D1, C2 and 10K resistor and to what will it connect? Jul 21, 2020 at 5:22
• Anytime, noviceFedora! You may use a breadboard and the jump wires that come with it. In a breadboard the rows are numbered 1,2,3... and the columns a,b,c...All the terminals on the same row are connected. The 'ground' ends of D1, C2 and the 10kΩ resistor are to be plugged in the same row. Jul 21, 2020 at 5:35