Crystal oscillator tester frequency counter kit review
Quite a few electronic kits can be purchased inexpensively from Aliexpress, in this post I’ll review this DIY frequency counter crystal oscillator tester:
Arrived in my mailbox 22 days after I placed the order, not bad. The kit came throughly packaged, unpacking it and removing from the anti-static bag, here are all the parts:
- 1 x 100 kΩ, 2 x 10 kΩ, 10 x 1 kΩ resistors
- 4 x 1N4148 diodes
- 3 x 22 pF ceramic capacitors
- 1 x 0.1 µF (104) capacitor, 1 x 0.001 µF (102) capacitor
- 5 x 7-segment LED displays 5611AH
- 20 MHz crystal
- DIP16 socket + Microchip PIC16F628A 8-bit PIC microcontroller
- S9014 NPN silicon transistor (pre-amplifier, low level & low noise)
- S9018 NPN silicon transistor (AM/FM amplifier, local oscillator FM/VHF)
- 7550A-1 high-current low-voltage 5 V voltage regulator
- variable capacitor (TODO: what range?)
- pushbutton
- 1x3 socket
- DC input jack barrel
A closer look at the PCB:
The board is labeled quite well, the silkscreen clearly indicating the component values. There are no reference designators or even a manual, unlike with the surface-mount kit I discussed in Surface-mount electronics for hobbyists: easier than you think, but neither were necessary — I had no trouble at all finding what component goes where, and the silkscreen also clearly indicated the component orientation. Anyways, let’s put this kit together.
Assembly
Inserting all the resistors:
There were ten 1 kΩ, two 10 kΩ, and one 100 kΩ, so I didn’t have to even read the resistor color code bands. Formed the leads, threaded through the pre-drilled plated through-holes, bent outward to hold into place. Inserting more of the components:
Flipped the board over, quickly soldered and trimmed each lead:
and soldered the remainder of components. This process completed quicker I expected, granted there is not much to this project. Here’s the end result:
Looks fairly close to the seller’s picture:
I only had to consult this picture to know where to solder the 3-pin socket. Not in the 3 holes labeled “+ - IN”, but the unlabeled holes nearby. Anyways, now that the kit is assembled, does it work?
Power
This kit comes with a center-positive barrel-style jack, measured about 3/8" square. No power adapter is provided, you’re on your own here. But any voltage source from 5–9 V should work.
Without a compatible wall wart, I soldered on wires to the + and - terminals, then wired to ground and +5 V from a Raspberry Pi breakout board. This worked fine, but I’d rather have something like a 9 volt battery clip instead, for portable usage. Like the MTester component tester I wrote about in Organizing electronic components. A battery clip or perhaps a USB power jack seems like an obvious improvement, wonder why they went with this obscure barrel connector instead. But it is only a minor flaw.
Cleaning the flux
I’ve soldered a decent number of boards by now, but have left the leftover rosin flux all over. About time to invest in some flux cleaner. Purchased a spray bottle of 91% isopropyl alcohol, sprayed it on and agitated with an old tooth brush a cotton swab. The flux appeared to instantly dissolve after spraying. Before, all that nasty flux all over:
and after cleaning with IPA:
much better. The alcohol left some sticky residue, I scrubbed much of it off but an improvement may be to also clean with acetone, as described in:
but for now, I’ll certainly be cleaning my boards with at least isopropyl.
Without further ado, time to test some crystals!
Quartz crystals
Over the years I have salvaged a couple crystal oscillators from various devices. They had been sitting in a box for years, not knowing what I would do with them. But they are fascinating components, commonly built from quartz, as detailed in this old but excellent 1964 film:
For the first test, I inserted a crystal labeled 27.000(10):
it works! The display reads “27.00”, indicating 27.00 MHz. Success.
Now that we know the circuit is functional, I tested all my other crystals:
- SUNNY 20, 27.000(10), 01–40(e): measured 27.00 MHz
- 5120.0 TEW 8G: measured 5.120 MHz
- 7.3728 UN 90 (the label partially was removed after desoldering a blob of solder on top of the metal case, and removing the flux, but it originally read 7.3728): measured 7.374 MHz, this is the first one slightly off
- SD33.8688: measured 33.87 MHz
This is hardly an impressive crystal collection, but it is neat to see they all were able to oscillate successfully near their specified frequency.
Ceramic resonators
Quartz crystal is the most-well known material for oscillators by far, used in quartz watches for precise timekeeping, I referred to it all the way back in SDR calibration via GSM FCCH using Kalibrate and LTE-Cell-Scanner on RTL-SDR and HackRF — but there is another material useful for oscillators: lead zirconium titanate (PZT), used in what are known as ceramic resonators.
Ceramic resonators are cheaper but less accurate (0.5% tolerance, compared to 0.001% for quartz crystals according to Wikipedia), so they can be used where frequency precision is not critical, such as CPU clocks. In fact, some computers even have a setting to intentionally spread the CPU frequency with the goal of reducing electromagnetic interference, spread spectrum:
I tested two ceramic resonators, as follows (note: center lead is ground):
- ZTT 12.00MT: measured 11.92 MHz or 11.91 MHz, within 0.67% of the intended 12.00 MHz. You could see the frequency oscillate between 11.92 MHz and 11.91 MHz, clearly a reflection of ceramic resonance inferiority.
- 4.00 Gd: Failed to measure any frequency, the tester only showed “0”
I also tested these components with MTester (see Organizing electronic components), and they were recognized as 43 pF and 54 pF capacitors, respectively:
which is not unexpected, given the construction of ceramic resonators may have some similarities to ceramic capacitors. MTester did not recognize any of the quartz crystals as anything, only showing “unknown/damaged/missing part”. Crystals/resonators are not supported by MTester (TODO: could MTester firmware be enhanced to measure freq?)
More quartz crystals
To supplement my meager salvaged quartz crystal collection, purchased:
arrived in 19 days in a small plastic bag:
Ordered two orders so I have two of each, dumped out the bags:
Measured each of the crystals, here they are listed by their label:
- (no label, presumably the 32.768 KHz): not tested, can’t fit in socket
- JWT4.000: ??? constantly varies drastically, can’t get a clear reading
- 6.000: 6.0010 MHz, 6.0009 MHz
- 7.3728: 7.3737 MHz, 7.3734 MHz
- 8.000: 8.0009 MHz, 8.0007 MHz
- 10.000: 10.001 MHz, 10.001 MHz
- 11.0592: 11.060 MHz, 11.060 MHz
- 12.000: 12.001 MHz, 12.001 MHz
- 12.288: 12.289 MHz, 12.289 MHz
- 16.000: 16.000 MHz, 16.000 MHz
- 20.000: 20.001 MHz, 20.001 MHz
- 22.1184: 22.120 MHz, 22.120 MHz
- 24.000: 24.002 MHz, 24.003 MHz
- 25.000: 25.002 MHz, 25.003 MHz
- 48.000: 0 (too high for the tester? but it is advertised as ≤50 MHz), 0
The crystal tester seller claims “1 Hz-50 MHz”, but I couldn’t read the 4 MHz or 48 MHz crystals accurately. Maybe it needs calibration by adjusting the variable capacitor? Attempted to turn it with a small Philips screwdriver, but while touched the display would reset, yet there was no visible adjustment to the frequency. From the manual:
and there is a programming mode, entered by long-pressing the pushbutton. The manual also says the crystal test range is “about 1M-45M”, although it does support measuring kilohertz signals (kHz frequencies are displayed as flashing, MHz as steady). With a 45 MHz maximum crystal test frequency, not being able to measure the 48 MHz crystal is not surprising.
Frequency counter
This device is a crystal oscillator tester, but also a frequency counter, see:
“-” and “+” connect directly to the 5–9 V power input connector, but “IN” connects to the PIC microcontroller. Instead of plugging in a crystal to the 3-hole socket (left), you can directly input an oscillating signal (right). The maximum signal input voltage is 5 V (not 5–9 V like the power supply input).
Square wave opamp
There are many ways to build an oscillator, some answers from /r/AskElectronics Circuit to transform DC~AC include a Wien bridge oscillator to generate sine waves, or other circuits for triangle and square waves.
I happen to have a LM324 quad operational amplifier chip, thanks to a salvaged Uninterruptible Power Supply, the gift that keeps on giving. Striking really how many useful components I salvaged from that humble UPS. Consulting the LM324 datasheet, chock full of useful applications, page 17:
if you look closely, you may notice the voltage divider — pointed out in the electro-tech-online op-amp square wave generator forums:
Since I built a bipolar ±5 V power supply already (see Surface-mount electronics for hobbyists: easier than you think), R2 and R3 can be omitted, instead I’ll put zero volts aka ground into +, and power the opamp with -5 V and +5 V. Only two resistors, R1 and R2 (both 100 kΩ) and one capacitor, C = 0.001 µF, are needed in addition to the LM324 (or whatever) opamp.
To listen to the square wave oscillations, I used an 8 Ω speaker and audio output transformer, assembled on a circuit board for Electronic project kits: hands on with a vintage 160-in-1. All three boards interconnected:
When powered up, I can hear a distinctive square wave sound:
but the question is: what’s the frequency?
Signal input header
The header for the frequency counter is unpopulated on this board, not included in the kit. I had a spare header, so I soldered it on:
Unipolar power
Since the frequency counter only accepts a maximum +5 V input signal, we have to add a voltage divider as in the original circuit anyways (or a voltage divider on the output), and remove the ±5 V power supply:
All of the resistors are 100 kΩ, and this circuit now works on a single +5 V power supply (square wave sound audible when connected to a speaker).
Counting the frequency
Finally, we can measure the frequency. The frequency counter is powered by +5 V, which directly connects through the 3-pin header to the opamp square wave oscillator, along with the signal input:
The frequency isn’t too stable, wasn’t expected to be, measures about 4.200 to 4.202, with a blinking decimal point (= kilohertz), looks reasonable. Resembles a generated 4002 Hz square in Audacity:
Conclusions
Overall I am quite satisfied with this do-it-yourself crystal oscillator tester / frequency counter kit. It is advertised as supporting up to 45 MHz, I was able to successfully test a 33.87 MHz crystal, but not 48 MHz. Lower frequency crystals are not as well-supported: allegedly 1 MHz is the minimum, but the lowest I could consistently measure was 5.120 MHz; couldn’t get a stable reading on a 4.000 MHz crystal.
However, the frequency counter signal input is able to count kilohertz signals with no problem. I built a square wave oscillator with an LM324 operational amplifier, and was able to measure the frequency at about 4 kHz.
The kit was easy to quickly assemble, composed of all through-hole components (but I wouldn’t mind a surface-mount version of this kit, would’ve been more useful than the practice LED kit built in Surface-mount electronics for hobbyists: easier than you think), and the end result is a useful tool for testing crystals and counting signal frequencies. My only gripes are about the unusual power supply barrel connector — should’ve used standard USB instead (TODO: try retrofitting it?), and the missing signal input header, but these are both only very minor deficiencies.
In conclusion, I definitely recommend this kit for anyone interested in building their own inexpensive crystal oscillator tester + frequency counter.
