frequency decades to volts - Page 1
Forum section: electronics / projects

author: RAPo
author_rank: Super Contributor
timestamp: February 04, 2024, 12:20:55 pm
content: Just a question:Is there an IC/schematics that converts frequency decades to discrete voltages?E.g 1,10,100,1kHz ...1MHz is converted to 0.1V,0.2V ... 0.7V.(should preferably work with a sine and square wave signal).

author: jonpaul
author_rank: Super Contributor
timestamp: February 04, 2024, 12:35:20 pm
content: You want a tachometer ckt.https://www.homemade-circuits.com/frequency-to-voltage-converter-circuit/AKA frequency to voltage converter F to V(eg monostable and integrator)https://www.analog.com/media/en/training-seminars/tutorials/MT-028.pdfF>>V>>Decades: comparators and resistor string like flash converter see schj

author: RAPo
author_rank: Super Contributor
timestamp: February 04, 2024, 12:55:55 pm
content: Thanks for the first link, that showed part of the puzzle:in that situation the signal must be passed through a Schmitt trigger before introducing it to the IC 4151 inputSo no all in one device/chip?

author: moffy
author_rank: Super Contributor
timestamp: February 04, 2024, 02:25:56 pm
content: Analog Devices have a number of ICs of which this is one:https://www.analog.com/media/en/technical-documentation/data-sheets/advfc32.pdf

author: RAPo
author_rank: Super Contributor
timestamp: February 04, 2024, 04:03:43 pm
content: Thanks much appreciated

author: PCB.Wiz
author_rank: Super Contributor
timestamp: February 04, 2024, 06:42:35 pm
content: Quote from: RAPo on February 04, 2024, 12:20:55 pmThe advfc32 is showing not for new designs.AD do have AD7740/AD7741/AD7742 showing as active, however most F-V parts I've see arelinear, you have asked forlog.You could add a log converter to a F-V part, however a MCU running a reciprocal frequency counter and DAC may be cheaper/better.DAC MCUs are under $1

author: RAPo
author_rank: Super Contributor
timestamp: February 04, 2024, 06:46:11 pm
content: Yes indeed I want alogconversion to volts. Thanks for your reply.

author: ejeffrey
author_rank: Super Contributor
timestamp: February 04, 2024, 07:07:57 pm
content: The trick with making an F-to-logV converter with a F-to-V followed by log is that the frequency and logV side have intrnisically huge dynamic range which will be hard to match with an intermediate linear voltage stage.If I wanted to do this entirely in the "analog" domain, I would look at building my own F-to-I converter with some sort of charge pump followed by a logarithmic I-to-V converter (which could be a simple diode connected transistor...) It's still going to be tricky to get a large dynamic range, but it will be easier than using an off-the-shelf F-to-V converter with buffered voltage output which are mostly designed for basically fixed range of operation, such as with a motor tachometer.A microcontroller frequency counter with a DAC would be the most flexible and highest dynamic range operation, but will probably have more latency and lower bandwidth than the analog solutions, at least at the high frequency end.You could also consider a hybrid. Use a programmable series of decade prescalers before the linear F-to-V converter, followed by standard log circuit. Then you have a microcontroller which monitors the output, and when it gets too high or too low, switches in/out a prescaler and also uses a DAC to add a DC offset to represent the decades eaten by the prescalers. In this way, the analog path only has to work accurately over ~2 decades at a time, but your frequency limit is only governed by how fast your prescalers can operate. The cost here is that there will be glitches when range switching, and without careful calibration those glitches could be pretty bad.

author: David Hess
author_rank: Super Contributor
timestamp: February 04, 2024, 07:17:56 pm
content: Quote from: RAPo on February 04, 2024, 12:20:55 pmThere are exponential voltage-to-frequency converters intended for music synthesizer applications, and a voltage-to-frequency converter can be used within a phase locked loop to make a frequency-to-voltage converter.

author: bson
author_rank: Unknown
timestamp: February 05, 2024, 08:23:10 pm
content: Quote from: RAPo on February 04, 2024, 06:46:11 pmLog with what base? Cascading a second priority encoder to the ladder shown above will give you log2.

author: kimballa
author_rank: Contributor
timestamp: February 07, 2024, 03:44:47 pm
content: For freq to current (F to I) conversion, you could look at the LM13700 which has such a tachometer circuit in the examples in the datasheet.Various electronic music synthesis pages also describe log conversion circuits for building voltage controlled oscillator (VCOs) using matched pair transistors that could be connected to the output.

author: RAPo
author_rank: Super Contributor
timestamp: February 07, 2024, 05:44:25 pm
content: The base is not that important, in the end it just a scaling factor.Quote from: bson on February 05, 2024, 08:23:10 pm

author: RAPo
author_rank: Super Contributor
timestamp: February 07, 2024, 05:46:35 pm
content: Yes that is one of the considerations. I would like to have seven decades.Will look into your idea.Quote from: ejeffrey on February 04, 2024, 07:07:57 pm

author: RAPo
author_rank: Super Contributor
timestamp: February 07, 2024, 05:48:13 pm
content: Thanks for the reference to the LM13700,Quote from: kimballa on February 07, 2024, 03:44:47 pm

author: mino-fm
author_rank: Regular Contributor
timestamp: February 08, 2024, 01:41:56 pm
content: A digital f/U-converter using ATtiny44 is limited up to 100 kHz:http://mino-elektronik.de/fmeter/fm_software.htm#bsp11Today I would use an RP2040 Pico-Board to do high resolution frequency measurement and DA-conversion by PWM.And it is just today, when I finished porting an older pico-fmeter project to Arduino-IDE.https://www.eevblog.com/forum/projects/pico-frequency-counter-using-rp2040/msg4151122/#msg4151122Input-pin for frequency measurement is pin 4 (GPIO2) of Pico-Board. I added a PWM-DA-output at pin 6 (GPIO4) of Pico-Board. A low-pass filter and voltage divider has to be added. PWM-frequency is 1,9 kHz.Input frequency range is down from 0,09 Hz up to 14 MHz. Sample rate is 100 sps or one period for lower frequency.Please take a look at line 121 of 'pico_fmeter.ino' to controll the scaling of PWM ratio. Data output is USB-connector only.

author: David Hess
author_rank: Super Contributor
timestamp: February 08, 2024, 11:39:06 pm
content: Below shows part of an analog only solution. The voltage-to-frequency converter shown below can be configured to produce a change in output frequency of a decade per volt. When placed inside of a phase locked loop, this relationship can be reversed, converting a change of a decade of frequency to an output change of 1 volt.I do not really recommend this analog method to exclusion, but it gives some idea of what would be required.Details of this circuit's operation are given in Linear Technology application note 14.

author: mino-fm
author_rank: Regular Contributor
timestamp: February 09, 2024, 11:47:37 am
content: Quote from: David Hess on February 08, 2024, 11:39:06 pm@ 1 Hz how long will it take to settle?1 hour, one day, one week?;-)

author: RAPo
author_rank: Super Contributor
timestamp: February 09, 2024, 12:12:22 pm
content: Thanks for the very useful information.Quote from: David Hess on February 08, 2024, 11:39:06 pm

author: David Hess
author_rank: Super Contributor
timestamp: February 09, 2024, 01:14:37 pm
content: Quote from: mino-fm on February 09, 2024, 11:47:37 amObviously not suitable to directly operate at 1 Hz, however a second PLL can be added to multiply the input frequency first allowing fast settling. Old frequency counters operated this way very successfully.