Post by thread:[EE]: PC Digitizing Storage Oscilliscope

Hi, Does anybody have any recommendations for a PC Digitizing Storage Oscilliscope, or just a regualr DSO. I have looked at Bitscope and the Link Instruments products, and also a board by Protek. I have also looked at the Instek brand of o-scopes. I am relatively new to this and would like something user friendly. My main use would be with PICs, so I assume the 20-40mhz range would suffice. Also, as this is a hobby, I was trying to keep the price <= $400. Thanks in advance, Kevin Apologies if this should be OT not EE. -- http://www.piclist.com hint: To leave the PICList spam_OUTpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu

> Does anybody have any recommendations for a PC Digitizing > Storage Oscilliscope, or just a regualr DSO. I've had my eye on the Electronics Australia Oct 1998 DSO. It has dual channel 20MSPS @ 8 bits, PC controlled timebase, vertical attenuation and vertical waveform position controls. It looks as though it could be built quite cheaply. Let me know if you want a schematic -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam@spam@mitvma.mit.edu

Jinx wrote: >> Does anybody have any recommendations for a PC Digitizing >> Storage Oscilliscope, or just a regualr DSO. > >I've had my eye on the Electronics Australia Oct 1998 DSO. It >has dual channel 20MSPS @ 8 bits, PC controlled timebase, >vertical attenuation and vertical waveform position controls. It >looks as though it could be built quite cheaply. Let me know if >you want a schematic > Thank you for the schematic, sir. I was most interested in the design of the analog front-end. This is always "the" major difficulty with this kind of project. The input amps can only accept Vin to +/-12v in direct mode, and the protection for overvoltage [470ohm series R + diodes clamping to +/-12v] is barely marginal. If you OV with 50v, you severely load down the signal, and can drive large currents into limiter resistors R20/R27 --> (50-12)/470 = 80mA --> 3W dissipation. There goes your 1 Mohm input resistance down the hollow pipe. thanks, - Dan Michaels Oricom Technologies http://www.oricomtech.com ========================= -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Dan: Do mind showing us your front end? -- Rich Dan Michaels wrote: {Quote hidden}> > Jinx wrote: > >> Does anybody have any recommendations for a PC Digitizing > >> Storage Oscilliscope, or just a regualr DSO. > > > >I've had my eye on the Electronics Australia Oct 1998 DSO. It > >has dual channel 20MSPS @ 8 bits, PC controlled timebase, > >vertical attenuation and vertical waveform position controls. It > >looks as though it could be built quite cheaply. Let me know if > >you want a schematic > > > > Thank you for the schematic, sir. I was most interested in the > design of the analog front-end. This is always "the" major > difficulty with this kind of project. > > The input amps can only accept Vin to +/-12v in direct mode, and > the protection for overvoltage [470ohm series R + diodes clamping > to +/-12v] is barely marginal. If you OV with 50v, you severely > load down the signal, and can drive large currents into limiter > resistors R20/R27 --> (50-12)/470 = 80mA --> 3W dissipation. > There goes your 1 Mohm input resistance down the hollow pipe. > > thanks, > - Dan Michaels > Oricom Technologies > http://www.oricomtech.com > ========================= > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

I'll show you mine if you'll show me yours ;-) about +V +-- 5pf--+ | | | | | | |-- >--+--+--100K--+--+-->| JFET (2N5486) | | | |-- | diodes ^ V | 1Meg | | | | | | +----->> to preamp | V V | (0 volts out for 0 volts in) V | |-- +-->| JFET (2N5486) | |-- | | | | +------+ | | -V -- Rich Dan Michaels wrote: {Quote hidden}> > At 12:45 PM 1/8/01 -0700, you wrote: > >Dan: > > > >Do mind showing us your front end? > > > >-- Rich > > > > People usually only make requests like this in the summertime, > after being out in the desert for a few hours without a hat :). > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Rich Ottosen wrote: {Quote hidden}>I'll show you mine if you'll show me yours ;-) > > > about +V > +-- 5pf--+ | > | | | > | | |-- > >--+--+--100K--+--+-->| JFET (2N5486) > | | | |-- > | diodes ^ V | > 1Meg | | | > | | | +----->> to preamp > | V V | (0 volts out for 0 volts in) > V | > |-- > +-->| JFET (2N5486) > | |-- > | | > | | > +------+ > | > | > -V > Does this mean [ie, because of the clamping diode connections] that the input dynamic range here is only +/-0.7v ??? Or I am not understanding it. [BTW, you don't want to see mine. The reason I never did this kind of project is because I could never figure out how to get 20 mhz BW, +/-50V input dynamic range, 1 Mohm input impedance, OV protection, and also NOT have to include a mechanical switch or relay - so I never did it]. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Silvio: I used this circuit at +/-5V myself. The limiting parameters are the Gate Source Cutoff Voltage and the maximum peak voltage that you need to buffer. For the 2N5486 the Gate Source Cutoff Voltage is 6.0 volts maximum which is too much for the +/-5V supplies. There is a similar part, the 2N5484 that cuts off at 3.0 volts. This should allow almost 2 volts of peak input/output swing. Another factor to consider is the Zero Gate Voltage Drain Current. For the 2N5486 it is 8ma to 20ma, for the 2N5484, it is lower at from 1ma to 5ma. This matters because this current is the idle current that the circuit draws. As a tradeoff, the higher operating current can drive a larger capacitive load at a higher frequency. My calculations show that the 1ma of the 2N5484 can drive 20pf of load from -2 volts to +2 volts in about 80ns which is about 4MHz of bandwidth. The 2N5486 would be several times faster but would need larger supply voltages. To keep the load on the buffer down to 20pf it should drive a single amplifier or comparator circuit. -- Rich T_BoNe wrote: {Quote hidden}> > How low voltage do this circuit work? > I need one that works with +/- 5V max... > > Silvio. > > Richard Ottosen gravada: > > > I'll show you mine if you'll show me yours ;-) > > > > about +V > > +-- 5pf--+ | > > | | | > > | | |-- > > >--+--+--100K--+--+-->| JFET (2N5486) > > | | | |-- > > | diodes ^ V | > > 1Meg | | | > > | | | +----->> to preamp > > | V V | (0 volts out for 0 volts in) > > V | > > |-- > > +-->| JFET (2N5486) > > | |-- > > | | > > | | > > +------+ > > | > > | > > -V > > > > -- Rich > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Dan Michaels wrote: {Quote hidden}> > Rich Ottosen wrote: > >I'll show you mine if you'll show me yours ;-) > > > > > > about +V > > +-- 5pf--+ | > > | | | > > | | |-- > > >--+--+--100K--+--+-->| JFET (2N5486) > > | | | |-- > > | diodes ^ V | > > 1Meg | | | > > | | | +----->> to preamp > > | V V | (0 volts out for 0 volts in) > > V | > > |-- > > +-->| JFET (2N5486) > > | |-- > > | | > > | | > > +------+ > > | > > | > > -V > > > > Does this mean [ie, because of the clamping diode connections] > that the input dynamic range here is only +/-0.7v ??? Or I am > not understanding it. > You are right. The circuit only allows about 1 volt peak to peak with the clamp diades as shown. Several diodes could be seriesed to increase the input voltage range. This is good because it also decreases the input capacitance. Another way is to use a pair of clamp voltage souces to bias the diodes to higher voltage. These voltages have to be less than the supply voltages. My needs were for the input of a frequency counter. Large dynamic range wasn't required since the following stage was a high speed comparator. The counter works out to about 70 MHz. Limited by the comparator and the TTL divide by 10 prescaler I used. > [BTW, you don't want to see mine. The reason I never did this > kind of project is because I could never figure out how to get > 20 mhz BW, +/-50V input dynamic range, 1 Mohm input impedance, > OV protection, and also NOT have to include a mechanical switch > or relay - so I never did it]. This is why Tektronix gets the big bucks. When I was in tech. school I obtained a set of books published by Tektronix on how to design oscilloscopes. They still used tubes in many of their examples but I would love have those books again. Maybe I need to try E-Bay -- Danger Will Robinson --. -- Rich > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Bit of a personal question isn't it? {Quote hidden}> -----Original Message----- > From: Richard Ottosen [SMTP:rottosenKILLspamIDCOMM.COM] > Sent: Monday, January 08, 2001 7:46 PM > To: .....PICLISTKILLspam.....MITVMA.MIT.EDU > Subject: Re: [EE]: PC Digitizing Storage Oscilliscope > > Dan: > > Do mind showing us your front end? > > -- Rich > > > Dan Michaels wrote: > > > > Jinx wrote: > > >> Does anybody have any recommendations for a PC Digitizing > > >> Storage Oscilliscope, or just a regualr DSO. > > > > > >I've had my eye on the Electronics Australia Oct 1998 DSO. It > > >has dual channel 20MSPS @ 8 bits, PC controlled timebase, > > >vertical attenuation and vertical waveform position controls. It > > >looks as though it could be built quite cheaply. Let me know if > > >you want a schematic > > > > > > > Thank you for the schematic, sir. I was most interested in the > > design of the analog front-end. This is always "the" major > > difficulty with this kind of project. > > > > The input amps can only accept Vin to +/-12v in direct mode, and > > the protection for overvoltage [470ohm series R + diodes clamping > > to +/-12v] is barely marginal. If you OV with 50v, you severely > > load down the signal, and can drive large currents into limiter > > resistors R20/R27 --> (50-12)/470 = 80mA --> 3W dissipation. > > There goes your 1 Mohm input resistance down the hollow pipe. > > > > thanks, > > - Dan Michaels > > Oricom Technologies > > http://www.oricomtech.com > > ========================= > > > > -- > > http://www.piclist.com hint: The list server can filter out subtopics > > (like ads or off topics) for you. See http://www.piclist.com/#topics > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Jinx wrote: >Attachment Converted: C:\WIN31APP\EUDORA\ATTACH\dsofront.gif Rich Ottosen wrote: {Quote hidden}> > about +V > +-- 5pf--+ | > | | | > | | |-- > >--+--+--100K--+--+-->| JFET (2N5486) > | | | |-- > | diodes ^ V | > 1Meg | | | > | | | +----->> to preamp > | V V | (0 volts out for 0 volts in) > V | > |-- > +-->| JFET (2N5486) > | |-- > | | > | | > +------+ > | > | > -V > I think a good modification for the ckt shown by Sir Jinx-GFW in his attachment might be to change R20 from 470 ohms to say 100K, and put a 20 pF cap across it, similar to what Rich shows above. The 100K should pass along DC/low-fequencies well, and the cap will pass the high end. You also get OV clamping without excessively loading down the input signal. I don't think I would want to use the SJ-GFW ckt as originally shown. - danM -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

>>Dan: >>Do mind showing us your front end? >>-- Rich Wow man...sometimes the air gets very fresh...the people get very lonely...how gay... :oD --------------8<-------Corte aqui-------8<-------------- All the best!!! Alexandre Souza EraseMExandinhospam_OUTTakeThisOuTinterlink.com.br Linux User #85093 --------------8<-------Corte aqui-------8<-------------- -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.