On 7/12/2016 4:54 PM, Dave Platt wrote:> In article <1siaobh469ijefbhiunll9l6hllnuvofer@4ax.com>, > John Larkin <jjlarkin@highlandtechnology.com> wrote: > >> It's an LS47, not an LS74. But that doesn't matter. > > You're right, I mis-read. But, as you say, it doesn't matter. > >> An LS input pulls itself up to about 1 volt, and weakly at that. That >> shouldn't bother the uP. > > The TI datasheet for the 74LS47 shows the equivalent input circuit as > having a resistor (nominal 20k) tied to Vcc, and then fed through a > zener to the input pin. It looks as if it'll try to pull up to "Vcc > minus one diode drop" - not all that strongly, but that may be enough > to pull the ATTiny's pin up above its absolute-maximum limit.MCU I/Os are typically protected by an ESD diode which will typically handle the current from 5 volts through a 20 kohm resistance which would be less than 100 uA. That's the real issue, the current through that diode. Too much and trouble. Until it blows, it won't let the voltage rise above the "danger" point. But your are right, this is not a good idea. Better to use one of many alternative solutions to the problem.> The O.P. may want to measure the Tiny's output-pin voltages, with the > 5-volt boost both on and off, and see if the chip's spec is being > violated. > > Assuming that the problem isn't due to a short circuit or miswiring > somewhere, the idea of switching to a CMOS 7-segment driver and > running the chip from the 3.3-volt supply would not be a bad > idea... this would honor the Tiny's absolute-maximum voltage ratings. > If I understand correctly, the 7-segment drivers are open-collector / > open-drain, and so the 7-segment display itself could be run directly > from the LiPo battery. This would avoid the need for a boost > converter, and should increase electrical efficiency - fewer > unnecessary volts to dissipate in the 7-segment current limiting > resistors, and so smaller resistors could be used. > > >-- Rick C
Driving 74LS from 3.3V uP
Started by ●July 12, 2016
Reply by ●July 12, 20162016-07-12
Reply by ●July 12, 20162016-07-12
On 7/12/2016 1:52 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?What about a driver chip that runs from 3.3 volts? TLC5916-Q1/TLC5917-Q1 -- Rick C
Reply by ●July 12, 20162016-07-12
On Tue, 12 Jul 2016 18:28:37 -0400, rickman <gnuarm@gmail.com> wrote:>On 7/12/2016 1:52 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? > >What about a driver chip that runs from 3.3 volts? TLC5916-Q1/TLC5917-Q1There's no problem with a 3.3v cmos uP driving 5 volt LS logic. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●July 13, 20162016-07-13
On Tuesday, 12 July 2016 18:57:00 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? > > > > I should add to be clear that there's no output on the display when the > bench supply goes into overcurrent, the open-collector output drivers > are not turning on.You might run into the same problem again when they do, due to filament cold resistance. You could soft start them. NT
Reply by ●July 13, 20162016-07-13
On Tue, 12 Jul 2016 13:52:29 -0400, 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?You are facing that eternal cosmic question: where the hell is the current going? -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●July 13, 20162016-07-13
On Wednesday, July 13, 2016 at 10:02:19 AM UTC-4, John Larkin wrote:> On Tue, 12 Jul 2016 13:52:29 -0400, 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? > > You are facing that eternal cosmic question: where the hell is the > current going?2x tubes at 14 segments with 20mA/segment gets you 14 x 5 x 20 = 1.4W which at 85% or less efficiency (Chinese special) = 1.65W or more from the LiPo or 1.65/3.5= 0.5A *average* with possible 1A peaks for the boost. Ckt is not the only thing hopelessly underpowered around here.> > > -- > > John Larkin Highland Technology, Inc > > lunatic fringe electronics
Reply by ●July 13, 20162016-07-13
On 07/13/2016 11:57 AM, bloggs.fredbloggs.fred@gmail.com wrote:> On Wednesday, July 13, 2016 at 10:02:19 AM UTC-4, John Larkin wrote: >> On Tue, 12 Jul 2016 13:52:29 -0400, 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? >> >> You are facing that eternal cosmic question: where the hell is the >> current going? > > 2x tubes at 14 segments with 20mA/segment gets you 14 x 5 x 20 = 1.4W which at 85% or less efficiency (Chinese special) = 1.65W or more from the LiPo or 1.65/3.5= 0.5A *average* with possible 1A peaks for the boost. Ckt is not the only thing hopelessly underpowered around here.It's only one tube. I tested the tube/converter circuit in isolation and it appears to light all the digit segment combinations of one tube OK
Reply by ●July 13, 20162016-07-13
On Wednesday, July 13, 2016 at 12:27:18 PM UTC-4, bitrex wrote:> On 07/13/2016 11:57 AM, bloggs.fredbloggs.fred@gmail.com wrote: > > On Wednesday, July 13, 2016 at 10:02:19 AM UTC-4, John Larkin wrote: > >> On Tue, 12 Jul 2016 13:52:29 -0400, 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? > >> > >> You are facing that eternal cosmic question: where the hell is the > >> current going? > > > > 2x tubes at 14 segments with 20mA/segment gets you 14 x 5 x 20 = 1.4W which at 85% or less efficiency (Chinese special) = 1.65W or more from the LiPo or 1.65/3.5= 0.5A *average* with possible 1A peaks for the boost. Ckt is not the only thing hopelessly underpowered around here. > > It's only one tube. I tested the tube/converter circuit in isolation and > it appears to light all the digit segment combinations of one tube OKThe bench supply is reacting to instantaneous current, so 2 segements is 40mA x 5/3.5/0.85= 67mA and possible 100mA current ripple peak in the boost inductor. Use a bigger PS or adjust that current limit upwards to 1A. There is no problem here, other than underpowered PS.
Reply by ●July 13, 20162016-07-13
On Wed, 13 Jul 2016 12:27:13 -0400, bitrex <bitrex@de.lete.earthlink.net> wrote:>On 07/13/2016 11:57 AM, bloggs.fredbloggs.fred@gmail.com wrote: >> On Wednesday, July 13, 2016 at 10:02:19 AM UTC-4, John Larkin wrote: >>> On Tue, 12 Jul 2016 13:52:29 -0400, 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? >>> >>> You are facing that eternal cosmic question: where the hell is the >>> current going? >> >> 2x tubes at 14 segments with 20mA/segment gets you 14 x 5 x 20 = 1.4W which at 85% or less efficiency (Chinese special) = 1.65W or more from the LiPo or 1.65/3.5= 0.5A *average* with possible 1A peaks for the boost. Ckt is not the only thing hopelessly underpowered around here. > >It's only one tube. I tested the tube/converter circuit in isolation and >it appears to light all the digit segment combinations of one tube OKAll segments from a cold start? -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●July 14, 20162016-07-14
On 07/12/2016 03:00 PM, Jim Thompson wrote:> On Tue, 12 Jul 2016 11:39:18 -0700, dplatt@coop.radagast.org (Dave > Platt) wrote: > >> In article <Hbahz.1$Dh7.0@fx13.iad>, >> 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. >> >> Are the ATTiny's pins 5-volt tolerant, when the chip is operated from >> a 3.3-volt supply? >> >> Based on what I see in the 74LS74 data sheet, the flip-flop's input >> pins are almost certainly going to be trying to pull the Tiny's >> output pins up to around 4.3 volts. This may very well be turning on >> some overvoltage-protection diodes in the Tiny. The 74LS74 >> data sheet suggests that Iil is limited to around 3.2 mA per pin, >> worst case, so 80 mA surprises me. >> >> ... Looking at the ATTiny85 data, it appears to me that it is *not* >> tolerant in this way. Absolute maximum voltage on any pin is limited >> to -0.5V, to Vcc+0.5V. So, you're overdriving it. >> >> You'll need a different sort of driver circuit to do this safely. > > Some of those old LS parts may draw significant crowbar currents as > the supply is ramped up... choking the "eBay special". > > ...Jim Thompson >I did some more experimenting this afternoon and I think something along these lines is the cause of the issue. Had the driver and incandescent display in isolation running from the bench supply at 3.7 volts. If I connect up the bench supply and then turn the power supply on from the switch, the circuit latches up and the supply goes into protection. If I allow the bench supply to start up, with the leads to the protoboard unconnected, and then connect the leads, the display and 74LS47 function normally.
