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For just under $ 7.00, you can buy the kit of this original audio level indicator from China's ICStation. 78 colourful LEDs display the level of an audio signal on a PCB measuring 25.2 cm by 2.0 cm. |
Introduction to the FED-202
The finished product of this kit
In the video below, you can see what the end result of this kit is. The FED-202 responds to a sound level that can either be picked up via the built-in microphone or provided via a standard audio connector. If no signal is present, two red LEDs light up in the middle of the PCB. If a signal is present, additional LEDs will light on the left and right. Obviously, the number of lit LEDs depends on the level of the audio signal.
The circuit is powered from a DC voltage between 3 V and 12 V and draws an average current of 120 mA from this supply voltage.
Important note
The fact that LEDs light up both left and right of the centre might give you the impression that the FED-202 is a stereo indicator. However, this is not the case! The left and right LEDs do exactly the same thing. Both channels of a stereo signal are mixed and it is this signal that drives the two LED columns.
Where to buy and what does it cost?
The FED-202 is offered under order number GY19569 for $ 6.99 on the site of the Chinese kit supplier ICStation. You pay only $ 5.00 shipping costs, and the package will be delivered in the Netherlands by DHL. Unfortunately, this supplier does not yet work with iDEAL, you need a credit card or an account on PayPal. The kit is also offered via Amazon, but there you will pay $ 16.47 for it, including shipping.
BEWARE! A smaller version is also available
On the German site of ebay, there is a provider called ‘binggogo’, which charges € 6.14 (including shipping) for a smaller version with only 40 LEDs. The main PCB is completely identical.
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| The large and the small version of the FED-202. (© 2025 Jos Verstraten) |
Delivery of the kit
The kit is delivered, without manual, in a plastic bag which in turn is enclosed in a sturdy envelope. The package fits through the letterbox.
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| The delivery of the FED-202. (© 2025 Jos Verstraten) |
The components supplied
The picture below shows all the components included in the package. The electronics are housed on two PCBs, which are connected by five six-pin connectors. Two short cables are included. One is a standard audio cable, the other an equally standard USB power cable.
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| All components of the FED-202. (© 2025 Jos Verstraten) |
The manual
The mail order company ICStation is, to our knowledge, the only Chinese kit supplier that really pays attention to the manuals that come with kits. They have taken the effort to produce an excellent eight-page manual in English that really describes every necessary step. Those manuals are publicly available on the supplier's internet site:
The two PCBs
In the picture below, you can see the two sides of the two PCBs. The small one is 12.5 cm by 2.0 cm and contains all components except the LEDs. The large one is 25.2 cm by 2.0 cm and contains only the 78 LEDs.
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| The two sides of the two PCBs. (© 2025 Jos Verstraten) |
The electronics in the FED-202
Unfortunately, ICStation does not disclose the schematic of this circuit. But based on the supplied components, something can of course be deduced about how the FED-202 works. There are only two ICs in the circuit, both copies of the well-known analogue LED driver LM3914. Such an IC compares the input voltage with ten voltage thresholds. The outputs of those comparators control ten LEDs. Clearly, one LM3914 drives the 19 left-hand columns with two LEDs each and the second drives the 19 right-hand columns with two LEDs each.
Furthermore, we find two transistors and an electret microphone. Probably, those two transistors are amplifiers that boost the output signal of the electret and the input voltage to the level needed to drive the two LM3914 chips.
Building the circuit
Assembling the main PCB
Based on the nineteen clear photos in the manual, soldering the main PCB should not be a problem for anyone. Pay attention to the polarity of the microphone! Two components, the adjustment potentiometer that sets the sensitivity of the circuit and the ON/OFF slide switch, are soldered to the copper side of the PCB.
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| The fully assembled main PCB. (© 2025 Jos Verstraten) |
Assembling the display board
There are three small bags with thirty LEDs each included in the package. All LEDs are transparent, so be careful not to accidentally mix them. Make sure that all LEDs rest completely flat on the PCB and stand in a nice, tight line. Solder the five PCB headers onto the copper side of this board.
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| The fully assembled display PCB. (© ICStation) |
The final assembly
This, of course, consists solely of plugging the two assembled PCBs together. On the large display PCB, there are four small mounting holes in the corners, but they are so close to the LEDs that they are unusable for mounting the PCB against the front panel of an audio amplifier, for example. Too bad! Four square centimetres of extra PCB could have prevented this!
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| The final assembly of the two PCBs. (© ICStation) |
A printable enclosure for the FED-202
Do you have a 3D printer? Then you can download two files you can use to make a nice enclosure for the FED-202. Those files are on the 'Thingiverse' site:
As the picture below shows, the electret microphone is now also soldered to the copper side of the control board.
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| The printable enclosure for the FED-202. (© Spudd1) |
The FED-202 in action
The sensitivity of the FED-202
We were curious to know how much signal you need to supply to the circuit to light all the LEDs. In the most sensitive position of the adjustment potentiometer, this turned out to be only 12.5 mV for a sinusoidal input signal of 1 kHz.
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| The frequency range of the FED-202. (© 2025 Jos Verstraten) |
The frequency response of the circuit
Since we were measuring anyway, we also measured the frequency range of this circuit. At the input we put sine waves from our Philips PM5109S generator, we noted the voltage for full scale output with our Philips mV-meter PM2454B. The frequency range of the FED-202 turns out not to be too good. As the table above shows, at 10 kHz it already requires more than double the voltage to drive all LEDs: 29.0 mV.
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FED-202 Audio Level Indicator Kit
FED-202 Audio Level Indicator Kit