On Fri, 15 Jul 2016 10:54:18 -0700 (PDT), tabbypurr@gmail.com wrote:>On Friday, 15 July 2016 14:56:28 UTC+1, bitrex wrote: >> On 07/15/2016 05:54 AM, piglet wrote: >> > On 14/07/2016 21:51, bitrex wrote: >> >> On 07/14/2016 04:27 PM, John Larkin wrote: >> >>> >> >>> Seven cold filaments could pull a lot of current. You could do >> >>> software tricks to soften the turn-ons, but the display might look >> >>> silly. >> >>> >> >>> >> >> >> >> I'm going to give preheating the filaments via PWMing the "shutdown" pin >> >> of the boost module a try, though I'll have to check the datasheet to >> >> see what the delay from a high level applied to that pin to output power >> >> good is. >> >> >> >> If that's not plausible I can try PWMing the "ripple blanking" input to >> >> the '47. >> > >> > Could be easier just to add resistors across LS47 outputs to preheat, >> > depending on ease of changing hardware vs software I suppose. >> > >> > piglet >> > >> >> I'm hoping to get a few PCBs of the circuit I'm working on made if it >> turns out alright, so I'd like to keep everything as compact as possible >> and do it in software if I can, rather than add a resistor network to >> the board. >> >> In the final design I'd like to ditch the LS chip entirely and simply >> use a uP of the same architecture with enough pins to handle all the >> segments directly. Many AVR chips are rated to sink 200mA to ground >> total through all pins, which surprised me a bit...though this circuit >> would push that limit and perhaps make me feel a little uncomfortable. >> >> I'd also like to dynamically adjust the voltage to the segments >> depending on how many are lit to increase battery life via PWM, but that >> may not be possible if the boost's enable pin can't handle being PWMed, >> so I may have to use a driver of some type. The cost/space advantage of >> using one 20 pin SOIC uC vs an 8 pin SOIC uC and a 16 pin SOIC is not >> gigantic. > >If PWM isn't an option there are other ways to reduce display current - though not greatly of course. Eg 2 output pins driving one filament, one via a resistor, or even a slightly adjustable voltage supply. Or an LDR/photodiode could adjust brightness according to ambient light etc. > > >NTThat's a good idea... turn on "warm" then full. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I'm looking for work... see my website.
Driving 74LS from 3.3V uP
Started by ●July 12, 2016
Reply by ●July 15, 20162016-07-15
Reply by ●July 15, 20162016-07-15
On 07/15/2016 03:01 PM, bloggs.fredbloggs.fred@gmail.com wrote:> On Friday, July 15, 2016 at 11:35:16 AM UTC-4, John Larkin wrote: >> On Fri, 15 Jul 2016 09:56:19 -0400, bitrex >> <bitrex@de.lete.earthlink.net> wrote: >> >>> On 07/15/2016 05:54 AM, piglet wrote: >>>> On 14/07/2016 21:51, bitrex wrote: >>>>> On 07/14/2016 04:27 PM, John Larkin wrote: >>>>>> >>>>>> Seven cold filaments could pull a lot of current. You could do >>>>>> software tricks to soften the turn-ons, but the display might look >>>>>> silly. >>>>>> >>>>>> >>>>> >>>>> I'm going to give preheating the filaments via PWMing the "shutdown" pin >>>>> of the boost module a try, though I'll have to check the datasheet to >>>>> see what the delay from a high level applied to that pin to output power >>>>> good is. >>>>> >>>>> If that's not plausible I can try PWMing the "ripple blanking" input to >>>>> the '47. >>>> >>>> Could be easier just to add resistors across LS47 outputs to preheat, >>>> depending on ease of changing hardware vs software I suppose. >>>> >>>> piglet >>>> >>> >>> I'm hoping to get a few PCBs of the circuit I'm working on made if it >>> turns out alright, so I'd like to keep everything as compact as possible >>> and do it in software if I can, rather than add a resistor network to >>> the board. >>> >>> In the final design I'd like to ditch the LS chip entirely and simply >>> use a uP of the same architecture with enough pins to handle all the >>> segments directly. Many AVR chips are rated to sink 200mA to ground >>> total through all pins, which surprised me a bit...though this circuit >>> would push that limit and perhaps make me feel a little uncomfortable. >>> >>> I'd also like to dynamically adjust the voltage to the segments >>> depending on how many are lit to increase battery life via PWM, but that >>> may not be possible if the boost's enable pin can't handle being PWMed, >>> so I may have to use a driver of some type. The cost/space advantage of >>> using one 20 pin SOIC uC vs an 8 pin SOIC uC and a 16 pin SOIC is not >>> gigantic. >> >> Well, you could fast-forward 40 years or so and use LED displays. > > Goes to show you really can't make stuff idiot proof.Haha, around here you need a state license for that level of passive-aggressiveness. I do appreciate the advice, though. ; )
Reply by ●July 15, 20162016-07-15
On 07/15/2016 03:15 PM, Jim Thompson wrote:> On Fri, 15 Jul 2016 10:54:18 -0700 (PDT), tabbypurr@gmail.com wrote: > >> On Friday, 15 July 2016 14:56:28 UTC+1, bitrex wrote: >>> On 07/15/2016 05:54 AM, piglet wrote: >>>> On 14/07/2016 21:51, bitrex wrote: >>>>> On 07/14/2016 04:27 PM, John Larkin wrote: >>>>>> >>>>>> Seven cold filaments could pull a lot of current. You could >>>>>> do software tricks to soften the turn-ons, but the display >>>>>> might look silly. >>>>>> >>>>>> >>>>> >>>>> I'm going to give preheating the filaments via PWMing the >>>>> "shutdown" pin of the boost module a try, though I'll have to >>>>> check the datasheet to see what the delay from a high level >>>>> applied to that pin to output power good is. >>>>> >>>>> If that's not plausible I can try PWMing the "ripple >>>>> blanking" input to the '47. >>>> >>>> Could be easier just to add resistors across LS47 outputs to >>>> preheat, depending on ease of changing hardware vs software I >>>> suppose. >>>> >>>> piglet >>>> >>> >>> I'm hoping to get a few PCBs of the circuit I'm working on made >>> if it turns out alright, so I'd like to keep everything as >>> compact as possible and do it in software if I can, rather than >>> add a resistor network to the board. >>> >>> In the final design I'd like to ditch the LS chip entirely and >>> simply use a uP of the same architecture with enough pins to >>> handle all the segments directly. Many AVR chips are rated to >>> sink 200mA to ground total through all pins, which surprised me a >>> bit...though this circuit would push that limit and perhaps make >>> me feel a little uncomfortable. >>> >>> I'd also like to dynamically adjust the voltage to the segments >>> depending on how many are lit to increase battery life via PWM, >>> but that may not be possible if the boost's enable pin can't >>> handle being PWMed, so I may have to use a driver of some type. >>> The cost/space advantage of using one 20 pin SOIC uC vs an 8 pin >>> SOIC uC and a 16 pin SOIC is not gigantic. >> >> If PWM isn't an option there are other ways to reduce display >> current - though not greatly of course. Eg 2 output pins driving >> one filament, one via a resistor, or even a slightly adjustable >> voltage supply. Or an LDR/photodiode could adjust brightness >> according to ambient light etc. >> >> >> NT > > That's a good idea... turn on "warm" then full. ...Jim Thompson >Assuming the switcher has the usual 1.2V reference, then a single open-drain MCU pin and a resistor can switch it between high and low output voltage. To simulate open drain, you write 0 to the bit in the register and toggle the output enable. Vout 0------R1R1R1---*--------*----0 FB | | R R 3 2 R R 3 3 | | | GND 0---------------* MCU pin (OD) Output off -> resistor R3 not connected -> low output voltage Output on -> resistor R3 connected -> high output voltage. The feedback pin doesn't go above 1.2V in normal operation. It'll jump up when R3 is disconnected, but should never go over 3.3V unless the voltage ratio is more than 2.5:1. If it is, a Schottky diode to the supply will fix it. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●July 15, 20162016-07-15
On Fri, 15 Jul 2016 08:35:11 -0700, John Larkin <jjlarkin@highlandtechnology.com> wrote:>On Fri, 15 Jul 2016 09:56:19 -0400, bitrex ><bitrex@de.lete.earthlink.net> wrote: > >>On 07/15/2016 05:54 AM, piglet wrote: >>> On 14/07/2016 21:51, bitrex wrote: >>>> On 07/14/2016 04:27 PM, John Larkin wrote: >>>>> >>>>> Seven cold filaments could pull a lot of current. You could do >>>>> software tricks to soften the turn-ons, but the display might look >>>>> silly. >>>>> >>>>> >>>> >>>> I'm going to give preheating the filaments via PWMing the "shutdown" pin >>>> of the boost module a try, though I'll have to check the datasheet to >>>> see what the delay from a high level applied to that pin to output power >>>> good is. >>>> >>>> If that's not plausible I can try PWMing the "ripple blanking" input to >>>> the '47. >>> >>> Could be easier just to add resistors across LS47 outputs to preheat, >>> depending on ease of changing hardware vs software I suppose. >>> >>> piglet >>> >> >>I'm hoping to get a few PCBs of the circuit I'm working on made if it >>turns out alright, so I'd like to keep everything as compact as possible >>and do it in software if I can, rather than add a resistor network to >>the board. >> >>In the final design I'd like to ditch the LS chip entirely and simply >>use a uP of the same architecture with enough pins to handle all the >>segments directly. Many AVR chips are rated to sink 200mA to ground >>total through all pins, which surprised me a bit...though this circuit >>would push that limit and perhaps make me feel a little uncomfortable. >> >>I'd also like to dynamically adjust the voltage to the segments >>depending on how many are lit to increase battery life via PWM, but that >>may not be possible if the boost's enable pin can't handle being PWMed, >>so I may have to use a driver of some type. The cost/space advantage of >>using one 20 pin SOIC uC vs an 8 pin SOIC uC and a 16 pin SOIC is not >>gigantic. > >Well, you could fast-forward 40 years or so and use LED displays.But would he get invited to the Whitehouse to show it off?
Reply by ●July 16, 20162016-07-16
On 07/12/2016 01:52 PM, bitrex wrote:> Prototyping a little toy for the kiddos out of junk box parts... > > I have a IV-9 Numitron connected up on a PCB to a 74LS47 BCD to 7 > segment driver. uP is a 3.3 volt ATTiny (Adafruit "Trinket" devboard) > powered via an on-board LDO directly off a 3.7 V 150mAh lipo. 3.7 volts > is boosted to around 5 to power the 74LS and Numitron segments via an > eBay special micro boost converter with shutdown pin. > > The test code right now simply outputs a BCD to the '47 inputs and pulls > the shutdown pin on the boost high to turn it on. > > The problem is the uP starts up fine and all the output voltages on the > 4 BCD pins looks good in isolation, but when the circuit is powered up > with the Numitron and '47 connected up the bench supply immediately > falls over into overcurrent protection at about 80 mA, way more than say > two incandescent segments to form the numeral 1 should be drawing at 5 > volts, I believe. > > The boost has plenty enough oomph to power all the Numitron digits from > either the LiPo or the bench supply, I tested that in isolation. > > Tested two different '47s with the same result. Not sure exactly what's > going on here...could there be some ESD/clamp diode pathway that's being > driven that I don't know about? Or a startup sequencing issue? >OK, so everything is working good now! I found that the boost's enable pin responds pretty quickly, so just ramping the ~5V supply voltage up via a PWM output to that pin, for about a half second, allows everything to start up well without any extra supply filtering.
Reply by ●July 16, 20162016-07-16
On Saturday, 16 July 2016 21:34:31 UTC+1, bitrex wrote:> On 07/12/2016 01:52 PM, bitrex wrote: > > Prototyping a little toy for the kiddos out of junk box parts... > > > > I have a IV-9 Numitron connected up on a PCB to a 74LS47 BCD to 7 > > segment driver. uP is a 3.3 volt ATTiny (Adafruit "Trinket" devboard) > > powered via an on-board LDO directly off a 3.7 V 150mAh lipo. 3.7 volts > > is boosted to around 5 to power the 74LS and Numitron segments via an > > eBay special micro boost converter with shutdown pin. > > > > The test code right now simply outputs a BCD to the '47 inputs and pulls > > the shutdown pin on the boost high to turn it on. > > > > The problem is the uP starts up fine and all the output voltages on the > > 4 BCD pins looks good in isolation, but when the circuit is powered up > > with the Numitron and '47 connected up the bench supply immediately > > falls over into overcurrent protection at about 80 mA, way more than say > > two incandescent segments to form the numeral 1 should be drawing at 5 > > volts, I believe. > > > > The boost has plenty enough oomph to power all the Numitron digits from > > either the LiPo or the bench supply, I tested that in isolation. > > > > Tested two different '47s with the same result. Not sure exactly what's > > going on here...could there be some ESD/clamp diode pathway that's being > > driven that I don't know about? Or a startup sequencing issue? > > > > OK, so everything is working good now! I found that the boost's enable > pin responds pretty quickly, so just ramping the ~5V supply voltage up > via a PWM output to that pin, for about a half second, allows everything > to start up well without any extra supply filtering.OK. Now what happens if your display goes from . to 8888? NT
Reply by ●July 17, 20162016-07-17
On 07/16/2016 06:38 PM, tabbypurr@gmail.com wrote:> On Saturday, 16 July 2016 21:34:31 UTC+1, bitrex wrote: >> On 07/12/2016 01:52 PM, bitrex wrote: >>> Prototyping a little toy for the kiddos out of junk box parts... >>> >>> I have a IV-9 Numitron connected up on a PCB to a 74LS47 BCD to 7 >>> segment driver. uP is a 3.3 volt ATTiny (Adafruit "Trinket" devboard) >>> powered via an on-board LDO directly off a 3.7 V 150mAh lipo. 3.7 volts >>> is boosted to around 5 to power the 74LS and Numitron segments via an >>> eBay special micro boost converter with shutdown pin. >>> >>> The test code right now simply outputs a BCD to the '47 inputs and pulls >>> the shutdown pin on the boost high to turn it on. >>> >>> The problem is the uP starts up fine and all the output voltages on the >>> 4 BCD pins looks good in isolation, but when the circuit is powered up >>> with the Numitron and '47 connected up the bench supply immediately >>> falls over into overcurrent protection at about 80 mA, way more than say >>> two incandescent segments to form the numeral 1 should be drawing at 5 >>> volts, I believe. >>> >>> The boost has plenty enough oomph to power all the Numitron digits from >>> either the LiPo or the bench supply, I tested that in isolation. >>> >>> Tested two different '47s with the same result. Not sure exactly what's >>> going on here...could there be some ESD/clamp diode pathway that's being >>> driven that I don't know about? Or a startup sequencing issue? >>> >> >> OK, so everything is working good now! I found that the boost's enable >> pin responds pretty quickly, so just ramping the ~5V supply voltage up >> via a PWM output to that pin, for about a half second, allows everything >> to start up well without any extra supply filtering. > > OK. Now what happens if your display goes from . to 8888? > > > NT >It can't, there's only one tube. It counts up from 0 to 9 and back down again in 1000 mS, 900, 800, etc. intervals well...
Reply by ●August 6, 20162016-08-06
On Wed, 13 Jul 2016 03:52:29 +1000, bitrex <bitrex@de.lete.earthlink.net> wrote:> Prototyping a little toy for the kiddos out of junk box parts... > > I have a IV-9 Numitron connected up on a PCB to a 74LS47 BCD to 7 > segment driver. uP is a 3.3 volt ATTiny (Adafruit "Trinket" devboard) > powered via an on-board LDO directly off a 3.7 V 150mAh lipo. 3.7 volts > is boosted to around 5 to power the 74LS and Numitron segments via an > eBay special micro boost converter with shutdown pin. > > The test code right now simply outputs a BCD to the '47 inputs and pulls > the shutdown pin on the boost high to turn it on. > > The problem is the uP starts up fine and all the output voltages on the > 4 BCD pins looks good in isolation, but when the circuit is powered up > with the Numitron and '47 connected up the bench supply immediately > falls over into overcurrent protection at about 80 mA, way more than say > two incandescent segments to form the numeral 1 should be drawing at 5 > volts, I believe. > > The boost has plenty enough oomph to power all the Numitron digits from > either the LiPo or the bench supply, I tested that in isolation. > > Tested two different '47s with the same result. Not sure exactly what's > going on here...could there be some ESD/clamp diode pathway that's being > driven that I don't know about? Or a startup sequencing issue? >meausre the R of the cold incandescent segments and you will your answer
Reply by ●August 7, 20162016-08-07
On 08/06/2016 06:08 AM, David Eather wrote:> On Wed, 13 Jul 2016 03:52:29 +1000, bitrex > <bitrex@de.lete.earthlink.net> wrote: > >> Prototyping a little toy for the kiddos out of junk box parts... >> >> I have a IV-9 Numitron connected up on a PCB to a 74LS47 BCD to 7 >> segment driver. uP is a 3.3 volt ATTiny (Adafruit "Trinket" devboard) >> powered via an on-board LDO directly off a 3.7 V 150mAh lipo. 3.7 >> volts is boosted to around 5 to power the 74LS and Numitron segments >> via an eBay special micro boost converter with shutdown pin. >> >> The test code right now simply outputs a BCD to the '47 inputs and >> pulls the shutdown pin on the boost high to turn it on. >> >> The problem is the uP starts up fine and all the output voltages on >> the 4 BCD pins looks good in isolation, but when the circuit is >> powered up with the Numitron and '47 connected up the bench supply >> immediately falls over into overcurrent protection at about 80 mA, way >> more than say two incandescent segments to form the numeral 1 should >> be drawing at 5 volts, I believe. >> >> The boost has plenty enough oomph to power all the Numitron digits >> from either the LiPo or the bench supply, I tested that in isolation. >> >> Tested two different '47s with the same result. Not sure exactly >> what's going on here...could there be some ESD/clamp diode pathway >> that's being driven that I don't know about? Or a startup sequencing >> issue? >> > > meausre the R of the cold incandescent segments and you will your answer"soft starting" the "enable" pin of the converter with PWM to bring up the voltage on the filament slowly got it sorted
