TD3X ( pi )

[DOOLEY]

just looked at that farnell link,

god,
some of them are expensive !!!


price varies from about £1.60 each to think about £12 !!!

home made is a good option then.

like I said, I just picked out a 25K LDR with a domed top,
filled the domed top flat,
same with an IR led,
dabbed with superglue and stuck e'm together.

finally covered with 2 tubes of shrink wrap and nipped the ends while
still soft so no external light could enter.

1st couple I made worked well.
so well they only needed a 33k resistor on the IR led.

opto-couplers I think are quite power hungry,
didn't want to waist 10ma driving the IR led just to alter the pitch.

so was quite happy when the homemade device was perfect with the 33k inline.

[Teleno]

An alternative to the LED + LDR is the following VCO (voltage controlled oscillator).

The control voltage sets the charging and discharging current of the capacitor C2 (through current mirrors Q1 - Q5), determining the oscillator's frequency and causing a 50% duty cycle for all frequencies.

[DOOLEY]

hello ivconic,
and all who are following this thread.


in june this year I made a new VLF detector with variable tone I.D.
(yes, will be posing it as soon as I have produced a prof pcb layout for it......)


anyways,
at first I was going to use a 4046 for the audio because it's easy to alter the pitch using variable voltage,
but,
I was unhappy with the quality of sound it was making,
and,
after thinking I would have to listen to the damd noise it made for a long time I opted for the good old 555.

I made a bit of a discovery,
well,
I think it was a discovery as NEVER seen it in print on ANY 555 notes.

anyways,
this evening I have breadboarded an alternative audio version for the TD3X.
this version removes the complication and trial and error surrounding the home made LDR / IRled.
I held back on posting this until id tried it in real life........

it's such a simple solution many of you will laugh !!!


right then,
below is a picture of the simple way to configure a 555 for 50/50 output.



so pretty standard 6/2 link,
and resistor from 6/2 to pin 3,
and produces very close to 50/50 duty.

so,
altering the voltage on pin 5 as we all know will alter the frequency / pitch output,
but,
duty cycle all goes to hell,
as the pitch goes up, the duty goes down and effectively makes the audio sound quieter.
as the pitch goes down, the duty goes up, it doesn't get louder, but just costs a lot of power wasted in the speaker,
things get hot etc etc.......

if only there was a way to play with the voltage on pin 5 AND keep the duty constant...........
the 555 IS a marvellous little chip........




and,
is all it took was a single resistor !!!

the 250k resistor is the key to it all.
just why a resistor that is 2.5X the value of the 555 feedback resistor works is anybody's guess,
poss some bright spark can explain.

few points to make,
ive used a TS555,
their internal resistor network comprises of 3 x 100k resistors,
as apposed to an NE555 which uses a network of 3 x 5k resistors,
so with the diagram ive posted don't use it on an NE555 as it prob wont work !!

anyways back to the chase,
ivconic,
simply alter the audio TS555 section to be like the 2nd diagram ive posted,
so pin 5 capacitor remains the same 100nf,
alter the 6/2 capacitor to 15nf,
the 150k feedback resistor needs altering to a 100k,
remove the homemade LDR/IRled, chuck it in the bin, AND THE 33K.
connect a 100k to the op-amp output that varies the pitch (the op-amp that used to feed the 33k to the IR led)
then,
most importantly,
swop over the feed to the pitch op-amp before the 10k's
this is essential as the 555 raises its pitch as the voltage on pin 5 is lowered.

altered TD3X audio section below :



100% tried the audio section and it works well.

pitch rests at 380hz and raises to a maximum of 720hz which should be equal to the LDR version.

duty cycle is more or less a constant 42%
so no wasted power,
no alteration of volume during pitch change,
and still pretty close to 50/50.

enjoy !!!



phew,
after writing all that i'm off for a brew !!!

[DOOLEY]

hello teleno,

you beat me to a solution by 13 minutes !!!

lol.



yup,
an elegant solution you have there,
I tried something similar a while back,
couldn't get my version to stay 50/50.

I fed with one transistor and discharged with another,
I rekon my early attempt that was charging the capacitor to 8v - the 0.7v npn drop,
and discharging to 0.7v,
didn't work due to the 555 on an 8v supply runs the capacitor between 5.33v and 2.67v,
and my early attempt wasn't "central"

[Teleno]

This is how to set the frequency of my 555 VCO:

Every time you double the control voltage, you double the frequency.

hello teleno,

you beat me to a solution by 13 minutes !!!

lol.



yup,
an elegant solution you have there,
I tried something similar a while back,
couldn't get my version to stay 50/50.

I fed with one transistor and discharged with another,
I rekon my early attempt that was charging the capacitor to 8v - the 0.7v npn drop,
and discharging to 0.7v,
didn't work due to the 555 on an 8v supply runs the capacitor between 5.33v and 2.67v,
and my early attempt wasn't "central"

You probably overlook that the transistors have to be configured as current sources/sinks of the same value.

[Davor]

An alternative to the LED + LDR is the following VCO (voltage controlled oscillator).

The control voltage sets the charging and discharging current of the capacitor C2 (through current mirrors Q1 - Q5), determining the oscillator's frequency and causing a 50% duty cycle for all frequencies.

This might work with CMOS 555 and with some emitter degeneration.
LTspice 555 is idealised and therefore the output goes from 0 to Vcc, but not so in RL. CMOS version is much closer to ideal, but you'll need some emitter degeneration anyway. You may seek a non-ideal model of 555 and try this with it, but don't be too disappointed.

[Teleno]

This might work with CMOS 555 and with some emitter degeneration.
LTspice 555 is idealised and therefore the output goes from 0 to Vcc, but not so in RL. CMOS version is much closer to ideal, but you'll need some emitter degeneration anyway. You may seek a non-ideal model of 555 and try this with it, but don't be too disappointed.

A high value of R2 makes sure the load on the 555's output is small. A resistor at the emitter of Q4 or Q6 (the one sourcing/sinking more current) equalizes the charge and discharge currents.

[Teleno]

This is how to set the frequency of my 555 VCO:

Correction:

[Teleno]

This version of the 555 VCO overcomes the problemes noted by Davor (thanks for pointing them out).

1. The actual low and high output voltage levels of the particular 555 implementation (CMOS or bipolar) no longer have an influence.

2. Only Q3 and Q4 need to be matched.



Oscillation frequency:

[Davor]

While this is much better than the circuit before, there is still a problem with matching transistors. Perhaps this is a candidate for CD4007 MOSFET array. Or moving to a completely different kind of VCO.

[Teleno]

While this is much better than the circuit before, there is still a problem with matching transistors. Perhaps this is a candidate for CD4007 MOSFET array. Or moving to a completely different kind of VCO.

There are nice matched PNP pairs for 40ct. at mouser.com (BCM847BV)

Tehre's also MMPQ6700 with two PNP and two NPN in one single package for $1.50.

A one-chip solution is the LM566 (obsolete) or LM567 (VCO part) or even the VCO in CD4046

[Orbit]

I do not understand you ! Dooley all finished and now some something calculate this what lay so far it realized,we all know formula !

https://www.youtube.com/watch?v=4GG-j5uKDTU

[Teleno]

Note that the VCO produces a pure triangular wave on pin 2 (TRIG) which has a nicer sound than a square wave.

You can compare the sounds of sine, square and triangle waves here.

[DOOLEY]

hello all,

many thanks teleno for offering alternative solution.


i'm not really in to formulas and equations................
the solution I proposed looks simpler .


on my simple approach ,
the 250k feeding the 6/2 link raises, or lowers the voltage to the timing capacitor inline with
the pitch altering voltage so that the duty cycle stays more or less fixed.

ok,
it's not 50/50 duty anymore,
but 42% is pretty close and sounds quite nice.

yes,
thought about using the wave from the 6/2 link for audio,
pretty close to a triangle wave.

doesn't go rail to rail though,
would have to use op-amp to achieve that,
just kept thing simple .

[Davor]

There are nice matched PNP pairs for 40ct. at mouser.com (BCM847BV)...

My point is not in line of what is possible on this blue planet, but what may be found in a first electronics shop you barge in. For many of us Mouser is as close as the Moon, and for the other part there are flat rate "fines" for ever wishing to buy anything there.
For that matter the home made vactrol is immensely better, because it is made from garden variety components, and it gives you opportunity to make it with your bare (bear?) hands. Most of us here are not in mass production, but a hobby.

There is also a matter of obsolescence. The most popular projects here are made from components that are in continuous production for the past 30 years or so. Exclusive or elusive components are perfect for a manufacturer that wishes to defer any attempts of reverse engineering. But a hobbyist is a different animal altogether. Say, OTAs. In 2005 Intersil set the status of vastly popular CA3280 OTAs to obsolete, which made many hobbyist spine shiver.

You can't count on commercial vactrols, but you can make your own. The most of the decent transistor arrays are extinct, and the remaining ones are mostly made of unobtainium.

There are other ways to skin a cat. I suggested you to include emitter degeneration resistors simply to avoid the transistor arrays. So instead of adding a few 100 ohm resistors that you already have, you insist on buying the arrays in Mouser, and wait a fortnight for them to arrive. Duh: