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Surrendering to the 555 Timer Option

Started by Ricky C May 11, 2020
On Tuesday, May 12, 2020 at 8:09:04 AM UTC-4, Michael Kellett wrote:
> On 12/05/2020 11:09, Ricky C wrote: > > On Tuesday, May 12, 2020 at 5:40:26 AM UTC-4, Michael Kellett wrote: > >> On 12/05/2020 02:57, Ricky C wrote: > >>> On Monday, May 11, 2020 at 9:29:28 PM UTC-4, whit3rd wrote: > >>>> 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... > >>>> > >>>>> Very slow timers are problematic in analog circuitry. > >>>> > >>>> The main problem, is parts count. It takes something like > >>>> three op amps to get a long risetime > >>>> by feeding 15 mV into a 1 Mohm/ 0.1uF integrator and detect > >>>> both the 1/4 time level-crossing, and do the reset at the > >>>> 4/4 time point. Half a dozen resistors. There's just a lot of > >>>> components to pick-and-place. Then there's the power problem: > >>>> an LT6002 micropower quad amp isn't bad, but isn't cheap, either. > >>> > >>> Not sure what that circuit would be doing. One of the first circuits I tried was a comparator with about half a dozen passives. A positive feedback resistor moves the Vth up and down on a voltage divider threshold at the positive input. To get different duty cycles a diode and resistor are paralleled with a resistor for the negative feedback to the cap. This is essentially the same as the two inverter loop, but instead of two inverters to provide different polarities to the resistor and cap a single comparator with two inputs do the same job. Instead of reversing the polarity of the cap relative to the single input, the comparator uses positive feedback to move the threshold. > >>> > >>> I would probably be using a comparator oscillator but I can't get them to simulate properly in LTspice. The cap should be charging to the positive input, but at lower Vcc it trips much sooner and mucks up the duty cycle a lot. I can't figure this out at all. I've tried every single comparator in the LTspice library thinking a voltage reference was getting in the way or something. None of them work properly at the low end of the specified voltage range. > >>> > >> > >> Huh ! > >> > >> Did you look at the model I posted ? > >> > >> You don't need the diode for 3:1 mark space, it does work on 2V in > >> LTSpice, uses an LTC1441 (dual), can drive 13mA, Iq about 5uA - what > >> more do you want ? > >> > >> The LTC1441 is a bit pricy but you could use any low power RRIO CMOS > >> comp (or op amp that's happy being a comp.). > >> > >> (Microchip do MCP6543 at $0.35 which has chip enable) - never had much > >> joy with running microchip models in LTSpice - but that wouldn't bother > >> me - and you are not having any joy simulating LT comps in LTSpice) > > > > Yes, thanks for your design. It does use two comparators with a number of discretes (8 or 9?) even if both parts are in one package, and has the problem in simulation I mentioned where the negative input from the capacitor will trip before it reaches the positive input level. That happens with every LT comparator I tried which was every one in the library. > > > > My design has a dual comparator with internal reference already for level sensing of the Vin and the Vbb on the supercap. Not that that means much. I suppose two different comparators could be used on the same design as opposed to an entirely different chip or the same comparators with a voltage reference added. They make comparators in quads, right? > > > > The 4060 seems like the best bet of all I've seen so far. Too bad I can't find a decent model. The comparator is a good solution too, but it really bugs me that I can't simulate it properly. There is something wrong that I am missing. > > > > I don't see a problem in LTSpice with the LTC1441 - and I carefully > checked the inputs at switching time - all looks OK. > > The Microchip model for the MCP6541 won't run in LTSpice. It runs in > Microchip's simulator - current (average) running = 3uA. Max output > current isn't great - you would need a MOSFET. > > If you use the MCP6543 with enable the BOM is: 1 chip, 4 resistors and 1 > cap, plus the "power" device. Almost no change in F from 2V to 5V, no > diodes. > > It should work with any RRIO comparator - but the Microchip one looks > pretty keen value unless you go Chinese. > > MK
I simplified the circuit so there just isn't anything to interfere unless I am missing something. A comparator oscillator with the cap (- input) not reaching the threshold (+ input) before the output switches. This is at 3 volts Vcc and it is about 0.1V shy. At 2 Vcc it is much worse, nearly 0.4V shy. In some simulations I saw the same problem with a lesser degree on the lower part of the cap waveform. You don't see this in your simulations? http://arius.com/temp/Alarm_osc_1_comb.pdf -- Rick C. -+- Get 1,000 miles of free Supercharging -+- Tesla referral code - https://ts.la/richard11209
On Tuesday, May 12, 2020 at 1:50:42 AM UTC-4, Ricky C wrote:
> On Tuesday, May 12, 2020 at 12:23:40 AM UTC-4, bitrex wrote: > > On 5/12/2020 12:19 AM, bitrex wrote: > > > On 5/11/2020 10:31 PM, Ricky C wrote: > > >> On Monday, May 11, 2020 at 10:11:56 PM UTC-4, bitrex wrote: > > >>> On 5/11/2020 9:13 PM, Ricky C wrote: > > >>>> On Monday, May 11, 2020 at 8:06:14 PM UTC-4, Jon Elson wrote: > > >>>>> edward.ming.lee@gmail.com wrote: > > >>>>> > > >>>>>> 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. > > >>>>> Plus at least 3 additional components, including a pretty large, > > >>>>> low-leakage > > >>>>> capacitor.  the ATTINY13A only requires a decoupling cap, and maybe > > >>>>> will run > > >>>>> without.  Also, getting large asymmetry of the on/off time can be > > >>>>> an issue > > >>>>> with the 555.  With the micro, you can get any time you want.  I am > > >>>>> not one > > >>>>> of those "put a micro in everything" guys, but this particular case > > >>>>> does > > >>>>> seem to warrant it.  In general, I don't like seeing RC timers with > > >>>>> delays > > >>>>> over a second. > > >>>> > > >>>> Normally I *am* one of the "digital is great" guys.  But in this > > >>>> case the design is for a ventilator which is mostly made of off the > > >>>> shelf electronics.  I am shooting for no use of anything that might > > >>>> not be so available down the road and the circuits should be easy to > > >>>> make in low tech processes.  So while programming MCUs are not > > >>>> exactly state of the art, I prefer to not use it if I can avoid it. > > >>>> There's also the issue of power supply.  When the thing is first > > >>>> powering up there is no voltage on the supercap.  I suppose I could > > >>>> use a couple of diodes to multiple source the MCU power.  I did look > > >>>> at the idea a while back since it is an obvious route.  I need at > > >>>> least two comparators which is not hard to find in MCUs either. > > >>>> > > >>>> The remaining part of the circuit is a constant current source to > > >>>> charge up the supercap.  I suppose that could be done by the MCU and > > >>>> a pass transistor.  If a PNP were used would that provide reverse > > >>>> current flow protection?  I suppose if the base were held at the > > >>>> collector voltage it would reverse bias the BE junction and prevent > > >>>> flow.  Otherwise the CB junction would be forward biased and the PNP > > >>>> would act as a very poor transistor still, no? > > >>>> > > >>>> I think the hard spec would be for the MCU to continue to work down > > >>>> to 2.0 volts or below.  I suppose a watch CPU would work at very low > > >>>> voltages, but then we are back to hard to source components.  How > > >>>> many MCUs are built to work over 2.0 to 5.25 volts with two > > >>>> comparators and/or an ADC? > > >>>> > > >>> > > >>> I reviewed the ventilator schematic that one company made public, you'll > > >>> be happy to know it uses a 555 timer! > > >>> > > >>> Other than that the business-end of the main board is not too > > >>> complicated; H-bridges to drive the blower motors and a bit of glue > > >>> logic. > > >>> > > >>> The rest of the commercial ventilator design is power supplies, a > > >>> relatively antiquated microprocessor board, display and display > > >>> driver/lighting circuitry, and boards with the chips for all the > > >>> external sensors that integrate mass airflow, velocity, O2 level, > > >>> respiration rate, and such into the microprocessor. > > >> > > >> Sounds a lot like what these guys are doing.  I don't know what they > > >> are using for the important sensors.  They have some kit type > > >> temperature sensor boards like they sell at the hobby shops.  Same for > > >> the H bridge, L298N.  Funny you can get modules from aliexpress > > >> cheaper than the chip at Digikey!  They seem to be using an Arduino > > >> Uno for the device controller.  Not sure what they are using for the > > >> display or controls yet. > > >> > > > > > > The commercial vent design looked both over-engineered and antiquated > > > simultaneously like a lot of medical/aerospace stuff. A lot of swish $2 > > > op-amps and comparators (maybe because it was designed to run off > > > battery-power for a while but for low frequency/DC tasks like they were > > > in not really necessary) doing pedestrian things plus an obscure > > > processor using external RAM and ROM like an embedded device from the > > > early 90s. > > > > Maybe they're only allowed to use "medical grade" op amps or something. > > IDK much about the standards for life-critical designs, not an area I > > would much like to get into. is there a "medical grade" 555? > > Medical equipment has to be proven to not harm the patient. It is not required to otherwise be fail safe. Military gear often has to continue working in spite of any single failure. That's a different animal indeed. > > I don't know what the restrictions are on this project. It is entirely possible it will never produce anything other than a hobby project. There are any number of alternative ventilator designs that simply were never produced for who knows what reason. One question I have not asked is even if they design this device and get someone to produce it, how do they know anyone wants to use it? Have they asked any of the end users what they need? What they require it to do and how it will fit into a medical setting. > > Not my problem. I'm just designing an alarm board. They might ask me to lay out other parts. > > -- > > Rick C. > > ++ Get 1,000 miles of free Supercharging > ++ Tesla referral code - https://ts.la/richard11209
IF you are considering a microprocessor, you may want to consider the TI MPS4xx. Ultra low power in sleep mode and relatively low power consumption in normal running mode. Getting a design approved for medical use, as you pointed out, takes a lot of rigor. That same level of rigor (if not more) is also required for any software device that the system should incorporate. If you are not knowledgeable in software and system safety design and analysis techniques, you are in for significant learning curve. Making an assurance case for systems based on software takes a significant amount of time. For medical systems IEC62304 is a good starting reference. If the device is Class C, the entire software development process is used to build an assurance case. Look at MIL STD 882E and DO178C for guidance as well. There is a whole lot more to design assurance than just slapping some code together. j
On 12/05/2020 13:50, Ricky C wrote:

> I simplified the circuit so there just isn't anything to interfere unless I am missing something. A comparator oscillator with the cap (- input) not reaching the threshold (+ input) before the output switches. This is at 3 volts Vcc and it is about 0.1V shy. At 2 Vcc it is much worse, nearly 0.4V shy. In some simulations I saw the same problem with a lesser degree on the lower part of the cap waveform. > > You don't see this in your simulations? > > http://arius.com/temp/Alarm_osc_1_comb.pdf >
My thresholds are a different proportion of the supply voltage and at 3V supply it looks fine. But at 2.5 it starts to go wrong. When I use your resistor values I get the same problem as you. https://www.dropbox.com/sh/hm6csu6y51rrb51/AADRBSgLEp7Y3alWs8nXRHVBa?dl=0 So due to my different component values it looked OK at three volts - but I agree with you - the model definitely doesn't work properly. MK
On 5/12/2020 9:32 AM, jjhudak4@gmail.com wrote:
> On Tuesday, May 12, 2020 at 1:50:42 AM UTC-4, Ricky C wrote: >> On Tuesday, May 12, 2020 at 12:23:40 AM UTC-4, bitrex wrote: >>> On 5/12/2020 12:19 AM, bitrex wrote: >>>> On 5/11/2020 10:31 PM, Ricky C wrote: >>>>> On Monday, May 11, 2020 at 10:11:56 PM UTC-4, bitrex wrote: >>>>>> On 5/11/2020 9:13 PM, Ricky C wrote: >>>>>>> On Monday, May 11, 2020 at 8:06:14 PM UTC-4, Jon Elson wrote: >>>>>>>> edward.ming.lee@gmail.com wrote: >>>>>>>> >>>>>>>>> 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. >>>>>>>> Plus at least 3 additional components, including a pretty large, >>>>>>>> low-leakage >>>>>>>> capacitor.  the ATTINY13A only requires a decoupling cap, and maybe >>>>>>>> will run >>>>>>>> without.  Also, getting large asymmetry of the on/off time can be >>>>>>>> an issue >>>>>>>> with the 555.  With the micro, you can get any time you want.  I am >>>>>>>> not one >>>>>>>> of those "put a micro in everything" guys, but this particular case >>>>>>>> does >>>>>>>> seem to warrant it.  In general, I don't like seeing RC timers with >>>>>>>> delays >>>>>>>> over a second. >>>>>>> >>>>>>> Normally I *am* one of the "digital is great" guys.  But in this >>>>>>> case the design is for a ventilator which is mostly made of off the >>>>>>> shelf electronics.  I am shooting for no use of anything that might >>>>>>> not be so available down the road and the circuits should be easy to >>>>>>> make in low tech processes.  So while programming MCUs are not >>>>>>> exactly state of the art, I prefer to not use it if I can avoid it. >>>>>>> There's also the issue of power supply.  When the thing is first >>>>>>> powering up there is no voltage on the supercap.  I suppose I could >>>>>>> use a couple of diodes to multiple source the MCU power.  I did look >>>>>>> at the idea a while back since it is an obvious route.  I need at >>>>>>> least two comparators which is not hard to find in MCUs either. >>>>>>> >>>>>>> The remaining part of the circuit is a constant current source to >>>>>>> charge up the supercap.  I suppose that could be done by the MCU and >>>>>>> a pass transistor.  If a PNP were used would that provide reverse >>>>>>> current flow protection?  I suppose if the base were held at the >>>>>>> collector voltage it would reverse bias the BE junction and prevent >>>>>>> flow.  Otherwise the CB junction would be forward biased and the PNP >>>>>>> would act as a very poor transistor still, no? >>>>>>> >>>>>>> I think the hard spec would be for the MCU to continue to work down >>>>>>> to 2.0 volts or below.  I suppose a watch CPU would work at very low >>>>>>> voltages, but then we are back to hard to source components.  How >>>>>>> many MCUs are built to work over 2.0 to 5.25 volts with two >>>>>>> comparators and/or an ADC? >>>>>>> >>>>>> >>>>>> I reviewed the ventilator schematic that one company made public, you'll >>>>>> be happy to know it uses a 555 timer! >>>>>> >>>>>> Other than that the business-end of the main board is not too >>>>>> complicated; H-bridges to drive the blower motors and a bit of glue >>>>>> logic. >>>>>> >>>>>> The rest of the commercial ventilator design is power supplies, a >>>>>> relatively antiquated microprocessor board, display and display >>>>>> driver/lighting circuitry, and boards with the chips for all the >>>>>> external sensors that integrate mass airflow, velocity, O2 level, >>>>>> respiration rate, and such into the microprocessor. >>>>> >>>>> Sounds a lot like what these guys are doing.  I don't know what they >>>>> are using for the important sensors.  They have some kit type >>>>> temperature sensor boards like they sell at the hobby shops.  Same for >>>>> the H bridge, L298N.  Funny you can get modules from aliexpress >>>>> cheaper than the chip at Digikey!  They seem to be using an Arduino >>>>> Uno for the device controller.  Not sure what they are using for the >>>>> display or controls yet. >>>>> >>>> >>>> The commercial vent design looked both over-engineered and antiquated >>>> simultaneously like a lot of medical/aerospace stuff. A lot of swish $2 >>>> op-amps and comparators (maybe because it was designed to run off >>>> battery-power for a while but for low frequency/DC tasks like they were >>>> in not really necessary) doing pedestrian things plus an obscure >>>> processor using external RAM and ROM like an embedded device from the >>>> early 90s. >>> >>> Maybe they're only allowed to use "medical grade" op amps or something. >>> IDK much about the standards for life-critical designs, not an area I >>> would much like to get into. is there a "medical grade" 555? >> >> Medical equipment has to be proven to not harm the patient. It is not required to otherwise be fail safe. Military gear often has to continue working in spite of any single failure. That's a different animal indeed. >> >> I don't know what the restrictions are on this project. It is entirely possible it will never produce anything other than a hobby project. There are any number of alternative ventilator designs that simply were never produced for who knows what reason. One question I have not asked is even if they design this device and get someone to produce it, how do they know anyone wants to use it? Have they asked any of the end users what they need? What they require it to do and how it will fit into a medical setting. >> >> Not my problem. I'm just designing an alarm board. They might ask me to lay out other parts. >> >> -- >> >> Rick C. >> >> ++ Get 1,000 miles of free Supercharging >> ++ Tesla referral code - https://ts.la/richard11209 > > IF you are considering a microprocessor, you may want to consider the TI MPS4xx. Ultra low power in sleep mode and relatively low power consumption in normal running mode. > Getting a design approved for medical use, as you pointed out, takes a lot of rigor. That same level of rigor (if not more) is also required for any software device that the system should incorporate. If you are not knowledgeable in software and system safety design and analysis techniques, you are in for significant learning curve. Making an assurance case for systems based on software takes a significant amount of time. For medical systems IEC62304 is a good starting reference. If the device is Class C, the entire software development process is used to build an assurance case. Look at MIL STD 882E and DO178C for guidance as well. > There is a whole lot more to design assurance than just slapping some code together. > j >
There was some question as to whether this company <https://www.medtronic.com/us-en/e/open-files.html> Would release the firmware for the ventilator design they public-domained as it might expose them to potential litigation risks, though it seems they were confident enough in it to do so. The cost of litigation regarding some kind of firmware flaw in a medical device like a ventilator and showing negligence to the standard required even by tort law would seem enormous. Have to do an independent review of the code and while rotten firmware killing otherwise healthy Toyota drivers was somewhat of a slam-dunk once the glaring issues were well-known, figuring out whether some particular bug (all code has them) in otherwise well-written ventilator firmware contributed to the injury or death of an already sick patient or not seems a tough row to hoe.
On Tuesday, May 12, 2020 at 9:32:47 AM UTC-4, jjhu...@gmail.com wrote:
> On Tuesday, May 12, 2020 at 1:50:42 AM UTC-4, Ricky C wrote: > > On Tuesday, May 12, 2020 at 12:23:40 AM UTC-4, bitrex wrote: > > > On 5/12/2020 12:19 AM, bitrex wrote: > > > > On 5/11/2020 10:31 PM, Ricky C wrote: > > > >> On Monday, May 11, 2020 at 10:11:56 PM UTC-4, bitrex wrote: > > > >>> On 5/11/2020 9:13 PM, Ricky C wrote: > > > >>>> On Monday, May 11, 2020 at 8:06:14 PM UTC-4, Jon Elson wrote: > > > >>>>> edward.ming.lee@gmail.com wrote: > > > >>>>> > > > >>>>>> 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?&nbsp; It is truly > > > >>>>>>> micropower, > > > >>>>>>> can > > > >>>>>>> be programmed in C, and has 5 general-purpose I/O pins.&nbsp; Your > > > >>>>>>> program > > > >>>>>>> should > > > >>>>>>> only be a couple lines of code.&nbsp; 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. > > > >>>>> Plus at least 3 additional components, including a pretty large, > > > >>>>> low-leakage > > > >>>>> capacitor.&nbsp; the ATTINY13A only requires a decoupling cap, and maybe > > > >>>>> will run > > > >>>>> without.&nbsp; Also, getting large asymmetry of the on/off time can be > > > >>>>> an issue > > > >>>>> with the 555.&nbsp; With the micro, you can get any time you want.&nbsp; I am > > > >>>>> not one > > > >>>>> of those "put a micro in everything" guys, but this particular case > > > >>>>> does > > > >>>>> seem to warrant it.&nbsp; In general, I don't like seeing RC timers with > > > >>>>> delays > > > >>>>> over a second. > > > >>>> > > > >>>> Normally I *am* one of the "digital is great" guys.&nbsp; But in this > > > >>>> case the design is for a ventilator which is mostly made of off the > > > >>>> shelf electronics.&nbsp; I am shooting for no use of anything that might > > > >>>> not be so available down the road and the circuits should be easy to > > > >>>> make in low tech processes.&nbsp; So while programming MCUs are not > > > >>>> exactly state of the art, I prefer to not use it if I can avoid it. > > > >>>> There's also the issue of power supply.&nbsp; When the thing is first > > > >>>> powering up there is no voltage on the supercap.&nbsp; I suppose I could > > > >>>> use a couple of diodes to multiple source the MCU power.&nbsp; I did look > > > >>>> at the idea a while back since it is an obvious route.&nbsp; I need at > > > >>>> least two comparators which is not hard to find in MCUs either. > > > >>>> > > > >>>> The remaining part of the circuit is a constant current source to > > > >>>> charge up the supercap.&nbsp; I suppose that could be done by the MCU and > > > >>>> a pass transistor.&nbsp; If a PNP were used would that provide reverse > > > >>>> current flow protection?&nbsp; I suppose if the base were held at the > > > >>>> collector voltage it would reverse bias the BE junction and prevent > > > >>>> flow.&nbsp; Otherwise the CB junction would be forward biased and the PNP > > > >>>> would act as a very poor transistor still, no? > > > >>>> > > > >>>> I think the hard spec would be for the MCU to continue to work down > > > >>>> to 2.0 volts or below.&nbsp; I suppose a watch CPU would work at very low > > > >>>> voltages, but then we are back to hard to source components.&nbsp; How > > > >>>> many MCUs are built to work over 2.0 to 5.25 volts with two > > > >>>> comparators and/or an ADC? > > > >>>> > > > >>> > > > >>> I reviewed the ventilator schematic that one company made public, you'll > > > >>> be happy to know it uses a 555 timer! > > > >>> > > > >>> Other than that the business-end of the main board is not too > > > >>> complicated; H-bridges to drive the blower motors and a bit of glue > > > >>> logic. > > > >>> > > > >>> The rest of the commercial ventilator design is power supplies, a > > > >>> relatively antiquated microprocessor board, display and display > > > >>> driver/lighting circuitry, and boards with the chips for all the > > > >>> external sensors that integrate mass airflow, velocity, O2 level, > > > >>> respiration rate, and such into the microprocessor. > > > >> > > > >> Sounds a lot like what these guys are doing.&nbsp; I don't know what they > > > >> are using for the important sensors.&nbsp; They have some kit type > > > >> temperature sensor boards like they sell at the hobby shops.&nbsp; Same for > > > >> the H bridge, L298N.&nbsp; Funny you can get modules from aliexpress > > > >> cheaper than the chip at Digikey!&nbsp; They seem to be using an Arduino > > > >> Uno for the device controller.&nbsp; Not sure what they are using for the > > > >> display or controls yet. > > > >> > > > > > > > > The commercial vent design looked both over-engineered and antiquated > > > > simultaneously like a lot of medical/aerospace stuff. A lot of swish $2 > > > > op-amps and comparators (maybe because it was designed to run off > > > > battery-power for a while but for low frequency/DC tasks like they were > > > > in not really necessary) doing pedestrian things plus an obscure > > > > processor using external RAM and ROM like an embedded device from the > > > > early 90s. > > > > > > Maybe they're only allowed to use "medical grade" op amps or something. > > > IDK much about the standards for life-critical designs, not an area I > > > would much like to get into. is there a "medical grade" 555? > > > > Medical equipment has to be proven to not harm the patient. It is not required to otherwise be fail safe. Military gear often has to continue working in spite of any single failure. That's a different animal indeed. > > > > I don't know what the restrictions are on this project. It is entirely possible it will never produce anything other than a hobby project. There are any number of alternative ventilator designs that simply were never produced for who knows what reason. One question I have not asked is even if they design this device and get someone to produce it, how do they know anyone wants to use it? Have they asked any of the end users what they need? What they require it to do and how it will fit into a medical setting. > > > > Not my problem. I'm just designing an alarm board. They might ask me to lay out other parts. > > > > -- > > > > Rick C. > > > > ++ Get 1,000 miles of free Supercharging > > ++ Tesla referral code - https://ts.la/richard11209 > > IF you are considering a microprocessor, you may want to consider the TI MPS4xx. Ultra low power in sleep mode and relatively low power consumption in normal running mode. > Getting a design approved for medical use, as you pointed out, takes a lot of rigor. That same level of rigor (if not more) is also required for any software device that the system should incorporate. If you are not knowledgeable in software and system safety design and analysis techniques, you are in for significant learning curve. Making an assurance case for systems based on software takes a significant amount of time. For medical systems IEC62304 is a good starting reference. If the device is Class C, the entire software development process is used to build an assurance case. Look at MIL STD 882E and DO178C for guidance as well. > There is a whole lot more to design assurance than just slapping some code together. > j
This design is so simple I can't see using an MCU. I could see using a GreenPak. But then I backed off of that too for the same reasons. Why require someone to program parts if it really wasn't needed? I think this entire design could be done in a single chip and a diode to prevent reverse current from the supercap to the input power rail. Maybe I should give the GreenPak a second look. It would be pretty interesting to do this in one chip. I bet I could get that to simulate ok!!! I say no MCU, but I'm going to take some time today to explore my options I guess. Another one chip solution sounds pretty good. Hmm... might not be one chip since there will need to be a way to program it and adding the USB chip to do that is pretty common these days. -- Rick C. -++ Get 1,000 miles of free Supercharging -++ Tesla referral code - https://ts.la/richard11209