Frequency-to-Voltage converter chip - Page 1
Forum section: electronics / projects

author: davorin
author_rank: Unknown
timestamp: February 02, 2025, 10:59:36 am
content: Good afternoon (o;Someone knows an inexpensive chip for converting frequencies in the range of 1MHz - 2MHz to voltage or can output a divided frequency for measuring with a small microcontroller?I need to pickup a RF signal wirelessly and detect with an ESP32 in which frequency range it currently is.From my SSA it looks like this with an unmatched antenna:

author: tggzzz
author_rank: Super Contributor
timestamp: February 02, 2025, 11:06:42 am
content: So the range is 2:1 (1MHz-2MHz), but...Signal level?Required accuracy?Required resolution?

author: davorin
author_rank: Unknown
timestamp: February 02, 2025, 11:10:55 am
content: My SA shows me -50dBm...but probably could be higher as the antenna picking up the signal isn't for this frequency range.Resolution for detection would be around 0.1MHz. So I can differentiate if the frequency is 1.4MHz or 1.5MHz with an accuracy of +/- 50kHz.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 02, 2025, 11:19:03 am
content: 1-2 MHz is easy to handle for most µCs without an extra divider. Only a µC with very low clock may want an extra divider.Most frequency to voltage converter chips are made for low frequencies, more like < 100 kHz.The question is more if the singal needs amplification (maybe filtering) for the µC to read it.

author: moffy
author_rank: Super Contributor
timestamp: February 02, 2025, 11:33:17 am
content: If you want a divider the 74LV393 can divide between 2,4,8 ... 256. You would need a comparator to square the signal first. The slower speed means you can use a slow micro but faster ARM chips like the STM32 range are quite inexpensive and many have special capture hardware for detecting periods, capture/timers.

author: davorin
author_rank: Unknown
timestamp: February 02, 2025, 11:45:32 am
content: My biggest concern is how to pick up the RF signal...Some FET input stage with a resonance circuit in front and a piece of wire?Have to pile up my electronics lab FETs and the like (o;

author: moffy
author_rank: Super Contributor
timestamp: February 02, 2025, 11:55:09 am
content: Because of the low frequency, something like a ferrite wound antena coil like the AM receivers, but you want it quite wideband, so you don't want a sharp resonance.

author: mikerj
author_rank: Super Contributor
timestamp: February 02, 2025, 11:55:27 am
content: Check out the olden (but golden)PIC based frequency meters, these could measure up to 50-60MHz with 5 digits resolution with no external pre-scaling. I'd suggest not using such old micros in your design, but the technique used is applicable to newer PICs and other micros.

author: tggzzz
author_rank: Super Contributor
timestamp: February 02, 2025, 12:10:08 pm
content: Quote from: davorin on February 02, 2025, 11:45:32 amYou have already stated the signal power, which is only useful in conjunction with a specific antenna.If you are using an antenna, then are you sure the stated signal strength represents the minimum and maximum input values? Typically those arehighlydependent on the environment in which the circuit operates.You will probably need some form of filtering, to reduce interfering signals affecting the measurement. The type and degree of filtering ishighlydependent on the environment in which the circuit operates. In particular you need to define and understand the consequences of in-band and out-of-band interfering signals, where "band" is the range in which your signal could occur.Summary: understanding radio channels, radio environments, radio receivers is not trivial; all figures are probabilities as a function of both time and position. That implies a probability that you will not detect a signal, which should be factored into your system design.

author: mino-fm
author_rank: Regular Contributor
timestamp: February 02, 2025, 03:52:42 pm
content: An ATtiny44 would work up to Fin <= 100 kHz; here it is limited to 5 kHz.http://mino-elektronik.de/fmeter/fm_software.htm#bsp11You could use a divider or adapt the program to another AVR (internal prescaler), a RP2040 Pico-board or STM32g0xx.

author: davorin
author_rank: Unknown
timestamp: February 02, 2025, 04:13:02 pm
content: I've ordered now some J-FETs and depletion MOSFETs from Digikey...as input amplifier and filter stage....Been a long time I've done analogue electronics (o;The microcontroller is already defined, as I need WiFi and maybe BT as well for configuration.

author: pqass
author_rank: Super Contributor
timestamp: February 02, 2025, 06:08:19 pm
content: You may be interested in the techniques used inthisreciprocal frequency counter.I've successfully re-implemented it (with mods) on an ATTINY84+LCD with a divide-by 256 (74HC4020) and D-FF (74HC74) front-end.I've tested it to about 30Mhz and is good to 7 digits with a 16MHz system clock but will work without the divide-by 256 if the input is less than the reference frequency.Though, your MCU will require two timers and an input capture unit.I didn't (yet) implement the FET amplifier parts. It could be an inspiration for you.

author: Zero999
author_rank: Super Contributor
timestamp: February 02, 2025, 07:15:46 pm
content: Doesn't the microcontroller have an internal counter/timer which can be used for this?If you need a Schmitt trigger, then use the 4060, which has an oscillator which can be repurposed as a Schmitt trigger.https://assets.nexperia.com/documents/data-sheet/74HC_HCT4060.pdf

author: PCB.Wiz
author_rank: Super Contributor
timestamp: February 02, 2025, 08:37:19 pm
content: Quote from: davorin on February 02, 2025, 10:59:36 amWhat does this signal come from, and how does it vary? What precision do you need?Your own MCU will radiate inside that band too, so a remote pickup cold make sense.A tuned LRC circuit and antenna, like on AM radios would help signal to noise.Parts like Nexperia 74AHC1G42xx osc+dividers are SOT packages with an unbuffered GATE in that can be AC coupled.

author: Sacodepatatas
author_rank: Regular Contributor
timestamp: February 03, 2025, 02:19:15 pm
content: Quote from: davorin on February 02, 2025, 10:59:36 amIn my country this is called an FM radio receiver. A very cheap logic IC that lets demodulate FM is the 74HCT4046.