Hi Oliver, you are right on everything. I got some 12F675 that if not using capture mode, I think they can be used in Timer1 gate mode (have to check it yet). 1/8000 means 125 useconds, I put that limit because some of the modern digital cameras have such high speeds, but in the practice for most of my cameras 1/1000 would be more than enough, so your recommendations are fully valid. Regarding phototransistors, you are also right. Photodiodes are faster, but normally they need an opamp behind to drive the digital ports. I got some BPW40 phototransistors, with a supply of 5volt a load of 100 ohm and a current of 5mA use to have raise and fall times of less than 50 uSec, that I think is enough for the 1/1000 case (1 mSec, 0.05% of the signal), so at first I'll try that. If I find any problems I'd switch over to the photodiode. And for the lighting I can use a standard led bulb DC driven, instead of the laser, you are right, the laser can overdrive the sensor, and may not be necessary. Kind regards and many thanks for the help. Jes.
On Sat, Sep 5, 2020 at 12:47 PM 'Oliver Seitz' via jallib < [email protected]> wrote: > Hi Jes! > > PIC12F1822 would be a nice candidate. 8 pins, one I2C, up to 32MHz on > Timer1. For your application I wouldn't use "Capture", but "Timer1 Gate". > > As resolution, you could think about 64µs (or 15625 Hz), it is 6.4% at > shutter 1/1000. Without crystal you won't get more garanteed than 2-3% > accuracy anyway. > > Without using interrupts, you could measure as long as (65536*64µs=) 4,19 > seconds. > > Ok, well if you have speeds down to 1/8000 (which I have never seen ;-) > can central shutters do that? ) you would need to use the interrupt method > to extend the timer. > > And... phototransistors are quite slow, especially then overdriven by > something like a laser. Might be worth thinking about using a photodiode. > > Greets, > Kiste > > Am Samstag, 5. September 2020, 12:08:40 MESZ hat Jes < > [email protected]> Folgendes geschrieben: > > > Thanks Rob. I'm not in a hurry, just learning and trying to get profit > from what I learn. > My project is a simple shutter speed meter for old film cameras (which I > collect and repair). > There is a little led laser pointing to a phototransistor sitting on the > film plane and going through the lens socket. Max shutter "speeds" (the > term is used in photography) are of 1/8000 of sec. On the other end, time > can be a long exposure of minutes or even hours, but normally measuring up > to 5 sec should be enough to certify the accuracy of the shutter. Most > pictures are taken in a range between 1/30 sec and 1/500 sec. Many old > cameras have a restricted range, not beyond 1/250 sec. > I would like to have an autonomous unit (not tied to a, computer) so I > would need only a few pins, just one for the signal and two for an small > I2C display, like the ones powered by the SSD1306 :O) > I was following the thread because that. > Now I have to find out if one of the small 12F units is able to do that. > Would be a perfect fit for my needs. > Kind regards. > Jes. > > El sáb., 5 sept. 2020 10:17, Rob CJ <[email protected]> escribió: > > Hi Jes, > > Since my previous project was finished I was thinking of prototyping this > frequency counter in JAL. My idea is to use it in combination with an > SSD1306 display and test it using the library I created for the Si5351 > although the range will be limited of this frequency counter. > > I think of making it 'auto ranging' as to increase the frequency range > indeed by changing prescaler values as you mentioned to measure lower > frequencies. I do not yet know how low it can measure. > > I might even post it on Instructables as prototype. I saw some examples > there based on Arduino but most of them are very simple, that is no > auto-ranging and so limited in the range it can handle. > > I started today, not sure how long it wil take but when it is done I will > post the source file on Jallib or on Instructables. > > BTW I will base it on a PIC16F1823 since that is the one I often use in my > projects but you can use other PICs as long as it has the capture function. > As said I do not know how long it will take so don't wait for it 🙂. > > Kind regards, > > Rob > > ------------------------------ > *Van:* [email protected] <[email protected]> namens Jesito's > μFabLab <[email protected]> > *Verzonden:* zaterdag 5 september 2020 09:55 > *Aan:* jallib <[email protected]> > *Onderwerp:* Re: [jallib] Some help needed to measure pulse length > > Many thanks Rob. I have to figure out how to do it. Is the timer working > at the MCU clock speed?. If so the 16 bit value might be too small to hold > the pulse length for i.e. a 5 sec pulse, isn't it?. I suppose some > prescaling should be done there... Have to investigate and read more on > that. > Kind regards. > Jes. > > > El jueves, 3 de septiembre de 2020 a las 18:51:51 UTC+2, > [email protected] escribió: > > Hi Jes, > > I just checked but I was mistaken, there is a procedure that calculates a > value for the timer based on a frequency. > > If you want to measure the length of a pulse you can use the capture mode > of a timer which is available in many PICs, for example the 16F1823.From > the datasheet: > Capture mode makes use of the 16-bit Timer1 > resource. When an event occurs on the CCP1 pin, the > 16-bit CCPR1H:CCPR1L register pair captures and > stores the 16-bit value of the TMR1H:TMR1L register > pair, respectively. An event is defined as one of the > following and is configured by the CCP1M<3:0> bits of > the CCP1CON register: > • Every falling edge > • Every rising edge > • Every 4th rising edge > • Every 16th rising edge > When a capture is made, the Interrupt Request Flag bit > CCP1IF of the PIR1 register is set. The interrupt flag > must be cleared in software. If another capture occurs > before the value in the CCPR1H, CCPR1L register pair > is read, the old captured value is overwritten by the new > captured value. > > Kind regards, > > Rob > > ------------------------------ > *Van:* [email protected] <[email protected]> namens Jes < > [email protected]> > *Verzonden:* donderdag 3 september 2020 13:45 > *Aan:* [email protected] <[email protected]> > *Onderwerp:* Re: [jallib] Some help needed to measure pulse length > > Thanks Rob, I look for it, just what I needed to know :0) > > El jue., 3 sept. 2020 12:01, Rob CJ <[email protected]> escribió: > > Hi Jes, > I thought there is already a Jal library to measure the width of a pulse > created by Matt. Would that do the job? > > Met vriendelijke groet, > Rob Jansen > ------------------------------ > *From:* [email protected] <[email protected]> on behalf of > Jesito's μFabLab <[email protected]> > *Sent:* Thursday, September 3, 2020 10:49:48 AM > *To:* jallib <[email protected]> > *Subject:* [jallib] Some help needed to measure pulse length > > Hello, > I'm new to JAL and I would like to measure the length of some pulses that > can be as long as 5 sec and as short as 1/8000 of second. > I have a handful of different pics, but ideally I would like to use a > small one, I just need one pin for the pulse, two more to interface to an > I2C small display and one more to reset and restart the measure. > Could anyone point me to an example that could guide me through this?. > I love the cleanless and simplicity of JAL. > Thanks in advance. > Jes. > > -- > You received this message because you are subscribed to the Google Groups > "jallib" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/jallib/29ca65ab-4f67-4e77-a321-9162fd396026n%40googlegroups.com > <https://groups.google.com/d/msgid/jallib/29ca65ab-4f67-4e77-a321-9162fd396026n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > > -- > You received this message because you are subscribed to the Google Groups > "jallib" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/jallib/AM0PR07MB62419C76A4D0F51F787AE7F5E62C0%40AM0PR07MB6241.eurprd07.prod.outlook.com > <https://groups.google.com/d/msgid/jallib/AM0PR07MB62419C76A4D0F51F787AE7F5E62C0%40AM0PR07MB6241.eurprd07.prod.outlook.com?utm_medium=email&utm_source=footer> > . > > -- > You received this message because you are subscribed to the Google Groups > "jallib" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/jallib/CAJSrQ%3Df1Lm6tHoKCfC4LW68OcQgsKw5FUeGQgaKaiag5oKV8EA%40mail.gmail.com > <https://groups.google.com/d/msgid/jallib/CAJSrQ%3Df1Lm6tHoKCfC4LW68OcQgsKw5FUeGQgaKaiag5oKV8EA%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > > -- > You received this message because you are subscribed to the Google Groups > "jallib" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/jallib/a079e103-5ea2-463a-b57d-53ad94caa730n%40googlegroups.com > <https://groups.google.com/d/msgid/jallib/a079e103-5ea2-463a-b57d-53ad94caa730n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > > -- > You received this message because you are subscribed to the Google Groups > "jallib" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/jallib/AM0PR07MB624194D03E0DB682805B8BF3E62A0%40AM0PR07MB6241.eurprd07.prod.outlook.com > <https://groups.google.com/d/msgid/jallib/AM0PR07MB624194D03E0DB682805B8BF3E62A0%40AM0PR07MB6241.eurprd07.prod.outlook.com?utm_medium=email&utm_source=footer> > . > > -- > You received this message because you are subscribed to the Google Groups > "jallib" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/jallib/CAJSrQ%3Df4shHgZ9P7ykPjWW2JVG%2BaFdsFV9QLp6QMCdQ16hP1Vw%40mail.gmail.com > <https://groups.google.com/d/msgid/jallib/CAJSrQ%3Df4shHgZ9P7ykPjWW2JVG%2BaFdsFV9QLp6QMCdQ16hP1Vw%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > > -- > You received this message because you are subscribed to the Google Groups > "jallib" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/jallib/100684801.1074600.1599302821173%40mail.yahoo.com > <https://groups.google.com/d/msgid/jallib/100684801.1074600.1599302821173%40mail.yahoo.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "jallib" group. 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