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Surrendering to the 555 Timer Option

Started by Ricky C May 11, 2020
I've looked at a number of different oscillators and either I can't bend them to my will because they are not very good oscillators or they aren't really amenable to simulation in LTspice.  

I need to turn on a sounder for 1 second out of 4.  A low going pulse is good as I'm using a driver FET even if it's not needed just to maximize the voltage range.  The circuit needs to be enableable with your choice of polarity from a totem pole driver.  The circuit needs to be low power, preferably less than 100 uA when operating and lower when disabled.  It has to work over a voltage range of 2 to 5 volts, lower is better.  With a current drive of mA from the enabling signal, I could just interrupt the ground to disable the circuit.  That would be low power standby for sure! 

I thought a couple of inverters with resistors, diode and cap like Win used would be good, but variations in the input threshold of the CMOS devices vary the duty cycle all over the map.  I saw in a TI document for one of their oscillator/counter chips they analyzed the timing error due to threshold differences in this circuit and found it to be small.  But that's only true for the full cycle, not the duty cycle.  

I suppose I could use a couple of FETs as an astable multivibrator (that has to be an old name from either a physical phenomenon or some electromechanical device).  I didn't find a circuit that was both simple and gave me confidence it would start up reliably.  

So that left me with the TI LMC555.  At 5 volts the Icc is 100uA typ, 240 uA max which is about the extreme upper limit to what I willing to work with.  The load it is controlling is only 3 mA.  I hate to burn up 10% of the power in the controller.  The other circuitry is only single digit uAs.  So if nothing else is found, the circuit will use a 555 timer.  At least it is easy to get a 4:1 duty cycle!  

-- 

  Rick C.

  - Get 1,000 miles of free Supercharging
  - Tesla referral code - https://ts.la/richard11209
On Monday, May 11, 2020 at 2:21:46 PM UTC+10, Ricky C wrote:
> I've looked at a number of different oscillators and either I can't bend them to my will because they are not very good oscillators or they aren't really amenable to simulation in LTspice.
Try this one. It's a vastly slowed down version of a low current 100kHz astable that I dreamed up back in 2008 and posted here in response to a rather silly request. John Fields came up with an equally silly solution, and I made his work with parts that you could actually buy. The point was that the BFR92 has very low internal capacitances, so it switches quite fast at very low current levels. Version 4 SHEET 1 2848 1240 WIRE -576 576 -736 576 WIRE -112 576 -576 576 WIRE -576 608 -576 576 WIRE -112 608 -112 576 WIRE -576 704 -576 688 WIRE -464 704 -576 704 WIRE -384 704 -464 704 WIRE -240 704 -320 704 WIRE -112 704 -112 688 WIRE -112 704 -240 704 WIRE -736 720 -736 576 WIRE -464 736 -464 704 WIRE -240 736 -240 704 WIRE -576 832 -576 704 WIRE -112 832 -112 704 WIRE -496 880 -512 880 WIRE -464 880 -464 816 WIRE -464 880 -496 880 WIRE -448 880 -464 880 WIRE -384 880 -320 704 WIRE -320 880 -384 704 WIRE -240 880 -240 816 WIRE -240 880 -256 880 WIRE -208 880 -240 880 WIRE -176 880 -208 880 WIRE -208 912 -208 880 WIRE -496 928 -496 880 WIRE -576 1008 -576 928 WIRE -496 1008 -496 992 WIRE -496 1008 -576 1008 WIRE -208 1008 -208 976 WIRE -112 1008 -112 928 WIRE -112 1008 -208 1008 WIRE -736 1040 -736 800 WIRE -576 1040 -576 1008 WIRE -112 1040 -112 1008 FLAG -112 1040 0 FLAG -576 1040 0 FLAG -736 1040 0 SYMBOL RES -592 592 R0 SYMATTR InstName R1 SYMATTR Value 1000K SYMBOL res -128 592 R0 SYMATTR InstName R2 SYMATTR Value 1000K SYMBOL cap -384 864 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName C1 SYMATTR Value 270n SYMBOL cap -256 864 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName C2 SYMATTR Value 820n SYMBOL VOLTAGE -736 704 R0 SYMATTR InstName V1 SYMATTR Value 5 SYMBOL npn -176 832 R0 SYMATTR InstName Q1 SYMATTR Value BFR92A SYMBOL npn -512 832 M0 SYMATTR InstName Q2 SYMATTR Value BFR92A SYMBOL res -256 720 R0 SYMATTR InstName R3 SYMATTR Value 4700K SYMBOL res -480 720 R0 SYMATTR InstName R4 SYMATTR Value 4700.1K SYMBOL cap -512 928 R0 SYMATTR InstName C3 SYMATTR Value 68n SYMBOL cap -224 912 R0 SYMATTR InstName C4 SYMATTR Value 330n TEXT -768 1176 Left 0 !.tran 0 20s 10s startup TEXT -776 1224 Left 0 ;This example schematic is supplied for informational/educational purposes only. TEXT -480 1176 Left 0 !.model BFR92A NPN(IS=0.1213E-15 VAF=30 BF=94.73 IKF=0.46227 XTB=0 BR=10.729 CJC=946.47E-15 CJE=10.416E-15 TR=1.2744E-9 TF=26.796E-12 ITF=0.0044601 VTF=0.32861 XTF=0.3817 RB=14.998 RC=0.13793 RE=0.29088 Vceo=15 Icrating=4m mfg=Infineon) -- Bill Sloman, Sydney
On 2020-05-11, Ricky C <gnuarm.deletethisbit@gmail.com> wrote:
> I've looked at a number of different oscillators and either I can't
bend them to my will because they are not very good oscillators or they aren't really amenable to simulation in LTspice.
> > I need to turn on a sounder for 1 second out of 4. A low going
pulse is good as I'm using a driver FET even if it's not needed just to maximize the voltage range. The circuit needs to be enableable with your choice of polarity from a totem pole driver. The circuit needs to be low power, preferably less than 100 uA when operating and lower when disabled. It has to work over a voltage range of 2 to 5 volts, lower is better. With a current drive of mA from the enabling signal, I could just interrupt the ground to disable the circuit. That would be low power standby for sure! CD4060 does an execellent low power oscillator, 3:1 can be got with a pair of diodes, but 2V is a bit low.
> I thought a couple of inverters with resistors, diode and cap like Win used would be good, but variations in the input threshold of the CMOS devices vary the duty cycle all over the map. I saw in a TI document for one of their oscillator/counter chips they analyzed the timing error due to threshold differences in this circuit and found it to be small. But that's only true for the full cycle, not the duty cycle. > > I suppose I could use a couple of FETs as an astable multivibrator (that has to be an old name from either a physical phenomenon or some electromechanical device). I didn't find a circuit that was both simple and gave me confidence it would start up reliably.
> So that left me with the TI LMC555. At 5 volts the Icc is 100uA typ, 240 uA max which is about the extreme upper limit to what I willing to work with. The load it is controlling is only 3 mA. I hate to burn up 10% of the power in the controller. The other circuitry is only single digit uAs. So if nothing else is found, the circuit will use a 555 timer. At least it is easy to get a 4:1 duty cycle!
ICM7555CBAZ 40uA at 5V https://www.renesas.com/us/en/www/doc/datasheet/icm7555-56.pdf -- Jasen.
On 11/05/2020 9:22 am, Jasen Betts wrote:
> > CD4060 does an execellent low power oscillator, 3:1 can be > got with a pair of diodes, but 2V is a bit low. >
Correct. The CD4060 is not spec'd below 3V but the 74HC4060 is most definitely spec'd from 2V to 6V. Assuming a osc frequency can be found where the HC4060 runs at low enough Idd to satisfy the OP then something like this might suffice .... <www.dropbox.com/s/l6aahkcdghpcxps/4060beeper1in4.jpg?raw=1> I drew a 2n7002 for the gate but that part will have too high Vgson for 2V use and a better choice substituted. piglet
On 11/05/2020 05:21, Ricky C wrote:
> I've looked at a number of different oscillators and either I can't bend them to my will because they are not very good oscillators or they aren't really amenable to simulation in LTspice. > > I need to turn on a sounder for 1 second out of 4. A low going pulse is good as I'm using a driver FET even if it's not needed just to maximize the voltage range. The circuit needs to be enableable with your choice of polarity from a totem pole driver. The circuit needs to be low power, preferably less than 100 uA when operating and lower when disabled. It has to work over a voltage range of 2 to 5 volts, lower is better. With a current drive of mA from the enabling signal, I could just interrupt the ground to disable the circuit. That would be low power standby for sure! > > I thought a couple of inverters with resistors, diode and cap like Win used would be good, but variations in the input threshold of the CMOS devices vary the duty cycle all over the map. I saw in a TI document for one of their oscillator/counter chips they analyzed the timing error due to threshold differences in this circuit and found it to be small. But that's only true for the full cycle, not the duty cycle. > > I suppose I could use a couple of FETs as an astable multivibrator (that has to be an old name from either a physical phenomenon or some electromechanical device). I didn't find a circuit that was both simple and gave me confidence it would start up reliably. > > So that left me with the TI LMC555. At 5 volts the Icc is 100uA typ, 240 uA max which is about the extreme upper limit to what I willing to work with. The load it is controlling is only 3 mA. I hate to burn up 10% of the power in the controller. The other circuitry is only single digit uAs. So if nothing else is found, the circuit will use a 555 timer. At least it is easy to get a 4:1 duty cycle! >
Here's an offer: Simulates in LTSpice except for some oscillatory strangeness in the supply current (but nowhere else which is odd !). Uses LTC1441 dual micropower comparator. I haven't tried it over voltage but shouldn't be too awful. I haven't bothered to tune it for you - not enough time while having lunch - but you'll work it out. Maybe Bill will derive a nice formula for R1, R2, R5 (set mark space) and R3, C1 and the others to set F. MK Version 4 SHEET 1 1092 680 WIRE -16 -176 -144 -176 WIRE 208 -176 -16 -176 WIRE 304 -176 208 -176 WIRE 624 -176 304 -176 WIRE 208 -128 208 -176 WIRE -144 -112 -144 -176 WIRE 208 -16 208 -48 WIRE 336 -16 208 -16 WIRE 432 -16 400 -16 WIRE 544 -16 512 -16 WIRE 768 -16 544 -16 WIRE 16 32 -80 32 WIRE 128 32 96 32 WIRE -16 80 -16 -176 WIRE 304 80 304 -176 WIRE -80 96 -80 32 WIRE -48 96 -80 96 WIRE 208 96 208 -16 WIRE 272 96 208 96 WIRE 128 112 128 32 WIRE 128 112 16 112 WIRE 480 112 336 112 WIRE -144 128 -144 -32 WIRE -48 128 -144 128 WIRE 272 128 160 128 WIRE -144 160 -144 128 WIRE 160 160 160 128 WIRE 160 160 -144 160 WIRE 208 192 208 96 WIRE -144 208 -144 160 WIRE 16 208 -144 208 WIRE 128 208 128 112 WIRE 128 208 96 208 WIRE -80 224 -80 96 WIRE 624 224 624 -176 WIRE 768 224 768 -16 WIRE -144 352 -144 288 WIRE -80 352 -80 288 WIRE -80 352 -144 352 WIRE -16 352 -16 144 WIRE -16 352 -80 352 WIRE 208 352 208 272 WIRE 208 352 -16 352 WIRE 304 352 304 144 WIRE 304 352 208 352 WIRE 624 352 624 304 WIRE 624 352 304 352 WIRE 768 352 768 304 WIRE 768 352 624 352 WIRE 304 400 304 352 FLAG 304 400 0 FLAG 544 -16 DISABLE FLAG 480 112 OUT SYMBOL Comparators\\LTC1441 -16 48 R0 SYMATTR InstName U1 SYMBOL voltage 624 208 R0 WINDOW 123 0 0 Left 0 WINDOW 39 24 124 Left 2 SYMATTR InstName V1 SYMATTR Value 3 SYMATTR SpiceLine Rser=0 SYMBOL res -160 192 R0 SYMATTR InstName R1 SYMATTR Value 1e6 SYMBOL res -160 -128 R0 SYMATTR InstName R2 SYMATTR Value 5e6 SYMBOL res 112 16 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 1e6 SYMBOL cap -96 224 R0 SYMATTR InstName C1 SYMATTR Value 1&Acirc;&micro; SYMBOL res 112 192 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 1e6 SYMBOL Comparators\\LTC1441 304 48 R0 SYMATTR InstName U2 SYMBOL res 192 -144 R0 SYMATTR InstName R6 SYMATTR Value 5e6 SYMBOL res 192 176 R0 SYMATTR InstName R7 SYMATTR Value 1e6 SYMBOL diode 400 -32 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D2 SYMATTR Value 1N4148 SYMBOL res 528 -32 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R8 SYMATTR Value 100k SYMBOL voltage 768 208 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value PULSE(0 3 10 1u 1u 10 20) TEXT -24 440 Left 2 !.tran 30 startup
Change D2 to BAT54 and R8 to 50k and works from 2.5V to 5V with about 
2.5% change in F.

MK
On Monday, May 11, 2020 at 4:15:58 AM UTC-4, Bill Sloman wrote:
> On Monday, May 11, 2020 at 2:21:46 PM UTC+10, Ricky C wrote: > > I've looked at a number of different oscillators and either I can't bend them to my will because they are not very good oscillators or they aren't really amenable to simulation in LTspice. > > Try this one. It's a vastly slowed down version of a low current 100kHz astable that I dreamed up back in 2008 and posted here in response to a rather silly request. > > John Fields came up with an equally silly solution, and I made his work with parts that you could actually buy. > > The point was that the BFR92 has very low internal capacitances, so it switches quite fast at very low current levels. > > Version 4 > SHEET 1 2848 1240 > WIRE -576 576 -736 576 > WIRE -112 576 -576 576 > WIRE -576 608 -576 576 > WIRE -112 608 -112 576 > WIRE -576 704 -576 688 > WIRE -464 704 -576 704 > WIRE -384 704 -464 704 > WIRE -240 704 -320 704 > WIRE -112 704 -112 688 > WIRE -112 704 -240 704 > WIRE -736 720 -736 576 > WIRE -464 736 -464 704 > WIRE -240 736 -240 704 > WIRE -576 832 -576 704 > WIRE -112 832 -112 704 > WIRE -496 880 -512 880 > WIRE -464 880 -464 816 > WIRE -464 880 -496 880 > WIRE -448 880 -464 880 > WIRE -384 880 -320 704 > WIRE -320 880 -384 704 > WIRE -240 880 -240 816 > WIRE -240 880 -256 880 > WIRE -208 880 -240 880 > WIRE -176 880 -208 880 > WIRE -208 912 -208 880 > WIRE -496 928 -496 880 > WIRE -576 1008 -576 928 > WIRE -496 1008 -496 992 > WIRE -496 1008 -576 1008 > WIRE -208 1008 -208 976 > WIRE -112 1008 -112 928 > WIRE -112 1008 -208 1008 > WIRE -736 1040 -736 800 > WIRE -576 1040 -576 1008 > WIRE -112 1040 -112 1008 > FLAG -112 1040 0 > FLAG -576 1040 0 > FLAG -736 1040 0 > SYMBOL RES -592 592 R0 > SYMATTR InstName R1 > SYMATTR Value 1000K > SYMBOL res -128 592 R0 > SYMATTR InstName R2 > SYMATTR Value 1000K > SYMBOL cap -384 864 R90 > WINDOW 0 0 32 VBottom 0 > WINDOW 3 32 32 VTop 0 > SYMATTR InstName C1 > SYMATTR Value 270n > SYMBOL cap -256 864 R90 > WINDOW 0 0 32 VBottom 0 > WINDOW 3 32 32 VTop 0 > SYMATTR InstName C2 > SYMATTR Value 820n > SYMBOL VOLTAGE -736 704 R0 > SYMATTR InstName V1 > SYMATTR Value 5 > SYMBOL npn -176 832 R0 > SYMATTR InstName Q1 > SYMATTR Value BFR92A > SYMBOL npn -512 832 M0 > SYMATTR InstName Q2 > SYMATTR Value BFR92A > SYMBOL res -256 720 R0 > SYMATTR InstName R3 > SYMATTR Value 4700K > SYMBOL res -480 720 R0 > SYMATTR InstName R4 > SYMATTR Value 4700.1K > SYMBOL cap -512 928 R0 > SYMATTR InstName C3 > SYMATTR Value 68n > SYMBOL cap -224 912 R0 > SYMATTR InstName C4 > SYMATTR Value 330n > TEXT -768 1176 Left 0 !.tran 0 20s 10s startup > TEXT -776 1224 Left 0 ;This example schematic is supplied for informational/educational purposes only. > TEXT -480 1176 Left 0 !.model BFR92A NPN(IS=0.1213E-15 VAF=30 BF=94.73 IKF=0.46227 XTB=0 BR=10.729 CJC=946.47E-15 CJE=10.416E-15 TR=1.2744E-9 TF=26.796E-12 ITF=0.0044601 VTF=0.32861 XTF=0.3817 RB=14.998 RC=0.13793 RE=0.29088 Vceo=15 Icrating=4m mfg=Infineon) > > -- > Bill Sloman, Sydney
Kind of sluggish looking, a good chance it will hang.
Ricky C wrote:


> I need to turn on a sounder for 1 second out of 4.
Why not use an ATTINY13A microcontroller chip? It is truly micropower, can be programmed in C, and has 5 general-purpose I/O pins. Your program should only be a couple lines of code. This chip casts about $0.50 in low quantity, a programmer can be had on eBay for about $10 and the development software is all free. Very slow timers are problematic in analog circuitry. Jon
On Monday, May 11, 2020 at 9:50:01 AM UTC-7, Jon Elson wrote:
> Ricky C wrote: > > > > I need to turn on a sounder for 1 second out of 4. > > Why not use an ATTINY13A microcontroller chip? It is truly micropower, can > be programmed in C, and has 5 general-purpose I/O pins. Your program should > only be a couple lines of code. This chip casts about $0.50 in low > quantity, a programmer can be had on eBay for about $10 and the development > software is all free.
555 timers goes for around 10 cents.
> Very slow timers are problematic in analog circuitry.
Only problem is selecting accurate capacitors. You can pre-select caps with freq counter. This should do 0.25 Hz at 25%: +----- VCC T(8) CNTL T(5) | RESET T(4) | -> R --- C <- 1 --- 2 | | +----+----- DIS T(7) GND | | D --- -> R T(3) OUT --+ 1 \ / <- 2 | | | TRIG T(2) -> R +----+---- THR T(6) <- 4 | | --- C +---- OUT --- 1 | +----- GND T(1) o o o o o o o o o o +-------+ +---+---------------+ o o o o x o o o o o R2 D1 R1 C1 T:555 C2 R4 180K 60K 2700nF 10nF +---+-------+-----------+ +---+ o o o o o o o o o o /----------------/ --+ -+ +---- | / / | +---+---+-------- +- /----+ | o o o o x o / o o o o -----------------------/ +-----------+
On 5/11/2020 12:21 AM, Ricky C wrote:
> I've looked at a number of different oscillators and either I can't bend them to my will because they are not very good oscillators or they aren't really amenable to simulation in LTspice. > > I need to turn on a sounder for 1 second out of 4. A low going pulse is good as I'm using a driver FET even if it's not needed just to maximize the voltage range. The circuit needs to be enableable with your choice of polarity from a totem pole driver. The circuit needs to be low power, preferably less than 100 uA when operating and lower when disabled. It has to work over a voltage range of 2 to 5 volts, lower is better. With a current drive of mA from the enabling signal, I could just interrupt the ground to disable the circuit. That would be low power standby for sure! > > I thought a couple of inverters with resistors, diode and cap like Win used would be good, but variations in the input threshold of the CMOS devices vary the duty cycle all over the map. I saw in a TI document for one of their oscillator/counter chips they analyzed the timing error due to threshold differences in this circuit and found it to be small. But that's only true for the full cycle, not the duty cycle. > > I suppose I could use a couple of FETs as an astable multivibrator (that has to be an old name from either a physical phenomenon or some electromechanical device). I didn't find a circuit that was both simple and gave me confidence it would start up reliably. > > So that left me with the TI LMC555. At 5 volts the Icc is 100uA typ, 240 uA max which is about the extreme upper limit to what I willing to work with. The load it is controlling is only 3 mA. I hate to burn up 10% of the power in the controller. The other circuitry is only single digit uAs. So if nothing else is found, the circuit will use a 555 timer. At least it is easy to get a 4:1 duty cycle! >
The 555 model that comes with LTSpice is behavioral and not very good, I don't think it models current draw very well for one thing. Get a full transistor-level model it's a simple chip shouldn't slow down sim time too much. Looks like maybe someone posted one... I have a gate-driver behavioral model from TI that doesn't work with a negative offset to the supply, e.g. +12 on Vcc and GND on Vee it works fine, but GND on Vcc and -12 on Vee and everything necessary referenced to Vee instead the model doesn't work at all - WTF