Electronics Bench in a Box

Tony Nixon posted [to the PICList] that he was able to write a boot loader for the '877 including a PC program to write code out to the PIC which would then write it to FLASH and run it. It dawned on me that a '877 preprogrammed with this boot loader was a $5 development environment when combined with the free MPLAB software and a few bench tools (power supply, DVM, signal generator, function generator, frequency counter, scope, logic probe or analyser, etc...) Then I started thinking that all these things have been implemented (at least in basic form) in PIC's. And the support electronics for a DVM and scope are very simular, as are the (variable) power supply and signal generator and the code for the function generator, frequency counter and scope all involve rapidly copying port values to or from ram, so....

The upshot is that I think a $10 board consisting of a '877, MAX 232, Analog front end, PWM output filters and power regulators could provide the following:

• Boot loader (see boot loader)(see boot loader)
• A port / register monitor
  • Ralph Stickley had already implemented a program to monitor register values over an available hardware serial port. His PC software polls the PIC with register numbers and receives a response via an ISR that consists of the current value of that register. You can get it at:
    http://www.piclist.com/stickleyregmon
  • [note that] one of the registers is the program counter and others are the ports, so....
• RS232 debugger / monitor?
  • if the PC software has a copy of the source code and hex file and the register monitor can see what the PC is pointing to....
  • I was wondering if the ISR could be setup to allow only one instruction of the main code to execute when the ISR returns. When the ISR regains the processor after that instruction, it could read the registers (one of them is the saved program counter, right? or wrong? I haven't worked with this, maybe it can't be read) report that to the PC which could then match the PC value against the code listing and display the listing with that line highlighted along with the other register values, port pin states, etc.. and buttons for single step, reset, etc..

    The ISR would loop checking the RS232 port and could also be capturing port pin signals, a2d results, etc.. and sending them to the PC which could display them on the screen in virtual logical analyzers, o'scopes etc...

    When the user presses the single step button, the single step command is sent by the PC to PIC and the ISR returns for one more main code instruction. If the user selected the Run button the ISR could still interrupt the main code every so many cycles and report to the PC the registers, ports, a2d etc... This would introduce a heck of a jitter in the main program but it would be better than not having it at all.

    If the user selected a register in the PC display the GUI would allow editing and then send a request to the PIC ISR which would update the register and continue looping.

  • Tony Nixon posted a start at
    http://www.infosite.com/%7Ejkeyzer/piclist/2000/Feb/1618.html
  • http://propic2.com/ is an ICD clone from Brazil
  • http://www.infosite.com/~jkeyzer/piclist/2000/Feb/index.html#1618
  • Scott Dattalo says the 18cxxx chips will have all the features necessary for a free ICD debugger see:
    http://www.infosite.com/~jkeyzer/piclist/2000/Feb/1718.html
    http://www.infosite.com/~jkeyzer/piclist/2000/Feb/1725.html
    http://www.infosite.com/~jkeyzer/piclist/2000/Feb/1858.html
  • Its been done! Closed source though. See:
    www.epemag.wimborne.co.uk/0300.htm
    http://www.epemag.wimborne.co.uk/0300.htm
    http://www2.iversoft.com/piclist/ViewMsg.php3?MsgID=200003091355.NAA24156@sp3at21.hursley.ibm.com
    http://www.infosite.com/%7Ejkeyzer/piclist/2000/Mar/0762.html
• Triggered high speed copy of pins to RAM with RS232 control / reporting for a super simple logic analyzer (2.5MHz max ~300x8 samples or 1Mhz and ~2400x1 samples per trigger)?
  • Dan Michaels of http://www.oricomtech.com has done this I hope code will be forthcomming.
  • http://www.infosite.com/%7Ejkeyzer/piclist/2000/Feb/1414.html Tom Handley designed a simple 24-Bit Trigger Comparator as part of a Logic Analyzer block that may be of use in a hight end version.
  • David Harris points out that AN689 on Microchip site describes an "Engineer's Assistant." Basically a logic probe + 1 bit analyzer + ASCII decoder + frequency counter with battery recharge circuitry (16F84+LCD). The logic analyzer acquisition software is a wonder to behold.
• A/D support for pic o'scope (20uS per sample gives 0-25kHz, ~300x8 to ~600x4 samples ) with display on PC via RS232?
  • SX based O’Scope from Alberto Geraci of BTX Systemas
  • http://www.people.cornell.edu/pages/shb7/posc.html Sean Hugh Breheny started a higher end version of such a thing
  • http://www.jwardell.com/about/seniorproj/index.html Josh Wardell is starting one for the Palm Pilot (very nice looking)
  • http://www.bitscope.com/  is a top end version. Not worth the extra cost for this but interesting anyway.
  • http://www.velleman.be makes a small O-SCOPE using a PIC16C65 and a 240x64 graphics LCD. The users manual has the schematic in the back.
• Audio Spectrum Analyzer fft/picspect.htm A PIC based Video display and Spectrum Analyzer
• DVM (0 to 5v, 10bits = ~3 digits single channel via A/D or multiple channel at lower res. via PWM capture with simple external hardware) display on PC via RS232?
  • http://www.chipcenter.com/circuitcellar/november99/c119dp1.htm PIC Base DVOM
  • http://www.infosite.com/%7Ejkeyzer/piclist/2000/Feb/0623.html Wagners list of options on front ends.
  • http://techref.massmind.org/microchip/16f877adsamp.htm 16F877 A/D sample program
• Function generator based on copy of RAM to port pins (2.5Mhz max ~170x8 or ~1Mhz and ~2400x1 steps) under PC control via RS232?
  • http://www.infosite.com/%7Ejkeyzer/piclist/2000/Jun/1245.html restricting the range of FSR by bit skip and clear/set
• Signal generator via PWM (?Hz low useful frequency ~300 waveform steps with simple external hardware RC) under PC control via RS232?
  • "Digital Frequency Synthesis" by Tom Napier in issue 99 (October 1998) of Circuit Cellar INK. Uses a PIC as a Digital Frequency Synthesizer. Richard Ottosen has developed an improved version for the Scenix SX ../scenix/sxncoex.zip
  • "AN-ECD06 - Precision 50-nsec Pulse Generation Using a PIC16C63" available at: http://www.oricomtech.com/appnotes.htm
  • The "Magic Sinewave" stuff from Don Landcaster http://www.tinaja.com may also apply.
• Regulated variable power supply with intelligent current limiting.
  • In the CUMP project, using an embedded controllers A/D out to bias a regulator was discussed
  • Connect one input of the comparitor on an SX18 or any of the PIC processors with a comparitor built in to a reference (input waveform, zener diode for constant voltage reference, or to DAC output from the uC itself) and the other to a resistor ladder (possibly a pot for variable gain) which scales down the output of the inverter to a 0-5v level and use the output to switch the mosfets. This is a voltage follower. The advantages are:
    • the PIC can measure the relative on-time to off-time and average that to monitor the amount of current being drawn by the load for overload protection.
    • the frequency of the ISR that updates the output based on the comparison at a regular interval can be tuned to match the transformers over varying loads and gains (since real world inductors do not respond equally over all current variations).
    • A DAC generated waveform would allow the PIC to function as a variable gain, high current, fsk function generator, extending the concept layed out in Tom Napier's article "Digital Frequency Synthesis" in issue 99 (October 1998) of Circuit Cellar INK and adapted to the SX by Richard Ottosen
    • the ability to switch the reference between an external waveform, an internal reference voltage and a DAC would allow the same device to function as an amplifier, current monitoring power supply and function generator.
    • When following an external waveform, it may be possible to record the duty cycle of the output over time and play it back later.

    http://www.xs4all.nl/~wf/wouter/pic/wisp/ has a nice charge pump design under PIC control. Not closed loop though.

• Device programmer (CUMP mode)
  • Given the ability to generate variable (high) voltages and the ability to control the pins, the device could be connected to other uC and memorys to program them. In this programming mode, the main PIC would regulate the high voltage power and stimulate the target PIC according to a programming procedure developed for the target device.
  • Maybe a ZIF or low cost socket on the main PIC's PCB. Maybe an optional daughter board that routes the main PIC pins and high voltage signals to the correct pins for the target using the main PCB socket or with a socket on the daughter board for other types of packages. Each low cost daughter card could (not must) have the target device ID and/or programming instructions for the main PIC in a serial EEPROM. Daughter cards could have stacking connectors to allow other cards to be connected at the same time.
  • http://www.piclist.com/cump the CUMP project

See also:

• http://members.cox.net/berniekm/super.html 16 functions with very few parts+
• http://www.bubblesoftonline.com
• http://www.htsoft.com
• http://www.piclist.com/projects.htm
• http://www.geocities.com/CapeCanaveral/Lab/9595/
• http://www.oricomtech.com/  is THE multi-function version. IR, Logic Analyzer (20Mhz), o'scope (400K, 5MHz repetitive), Glitch mode, Serial Protocals (to 5Mhz), Function Generator (5Msps, 50 nsec pulse), Signal Generator (Arbitrary Wave or Multi-Pulse), Delayed Triggering (1 - 1000 usec), Pulse count (120 Mhz) $199 limited time!
• http://www.oricomtech.com/projects.htm New lower cost version of the hardware
• http://www.bitscope.com/  is THE top end version. Dual channel 100 Mhz Digital Sampling Oscilloscope and 8 channel Logic Analyzer. Really clean user interface software. The entire design is open and available for download free of charge. Board level kit is $250. Main chips and PCB for $70.
• http://204.210.50.240/techref/default.asp?url=tools.htm

Anyway, you could develop right on the CUMP and then port it to a (smaller, cheaper) target processor which you program, stimulate and test via the CUMP after the code is basically running. See http://www.adv-transdata.com/User_Guide/DS91033.pdf (cached 20000229114401)

Optional extensions are without limit. Starting from a low cost, easy base, the unit could be cheaply extended to add external high speed RAM signal capture and generation, high impedance analog front ends and back ends, user interfaces to replace the PC GUI. If the daughter card interface is done correctly, these additions would be as easy as plugging in a new card with the code for the main processor to use it right on the daughter cards own EEPROM.

An external, high speed (hundreds of MHz) oscillator with a high speed counter (maybe the timers in the SX48/52) might be capable of adding TDR capability. Most 50 ohm coaxial cable has a V factor of .66, and the pulse goes out and comes back, so figure .33C as a starting point. At 300 MHz, a wavelength in free space is 1M, so to get accuracy to the nearest meter, you'd have to count at 600*.33 or 200 MHz. Other cables are different, basically the higher the Z, the higher the C.

Build a 110VAC to 1V switcher, use 'flat-transformer' technology for 98% or better efficiency. With this type transformer, there is almost zero leakage inductance, so almost no losses from snubbers, etc. in the primary. Flat transformers don't even need square 50/50 duty cycle...you can regulate by varying the on time of the input voltage switches. They have a limitation of fifteen volts, but yield an easy way to build a 300kHz to 1 MHz switcher.

On the secondary, be sure to use Power Mosfets as synchronous rectifiers, so that ON resistance is perhaps .05 Ohms when they conduct and diode losses are virtually non-existent. In other words, you drive the Mosfets on only when the diode they replace is supposed to conduct. Terrific efficiency. Output voltage or current is easy to control depending on the feedback circuit used. We are talking 98% efficiency here with 1.0 volts out, scalable to almost any power level.

Dan Michaels says:

I've done a number of the things you mention using 20Mhz PIC16C73/74/76 chips. They make rather nice simple 1-chip scope/logic_analyzer/generator instruments - albeit a little slow.

The best "logic analyzer" rate is 2.5Mhz using a 20Mhz part. 1 instr to capture, 1 to store, using linear code and direct addressing. You can't fill more than about 96+80=176 locations without bank-fiddling, which adds some skew. The best rate I could coax out of 1-bit sampling, which of course requires time to pack 8-bits to a byte, was 1 Mhz.

If you can actually get 20Mhz and 5 Mhz datacq, as mentioned in your e-mail, please tell me how.

Also, regarding "signal generator via PWM", this works extremely well on the 2nd gen PICs with the built-in PWM generator. Turns out all period values and duty-cycles are available on these chips, so you are not limited to just a few PWM rates (as on most microcontrollers??), and you can actually get continuous pulse widths and reprates from 50ns @ 5Mhz, down to about 800us @ 1.2Khz. Since, it's done in h.w., there is no s.w. overhead or timing loop problems.

A while back, I wrote an Appnote about this, which spells it out in detail:

"AN-ECD06 - Precision 50-nsec Pulse Generation Using a PIC16C63" available at: http://www.oricomtech.com/appnotes.htm

- Dan Michaels
Oricom Technologies

Power@

See also:

• http://www.teslaco.com where they combined a buck and boost stage into one unit with a coupling cap and a special inductor and got 90 percent efficiency and virtually eliminated ripple. They published an article in a robotics magazine many years ago.
• A Low-Cost High-Performance DC-DC Converter Topology
• http://www.tran.hammfg.com/
• http://www.virtualbreadboard.com/PICIO.htm
• http://www.infosite.com/%7Ejkeyzer/piclist/2000/Feb/1326.html
• http://www.dontronics.com/picex.html

Questions:

• +
• Daniel Imfeld asks: " All the links to www.infosite.com are gone. Does anyone know if these pages have been mirrored elsewhere?" James Newton replies: http://web.archive.org/*/http://www.infosite.com

  But the web archive is not accessible from that. Use the PICList.com archive instead. Translating the one to the other should be pure hell. I * think * the number at the end of the link is the counted number of the post since the beginning of the month. The month view in the PICList.com archive might help you get near the right point....

  If you were willing to help fix up the links, I could modify the archive browser to show a cumulative count for each day from the first of the month as well as the count per day.+

  +

• @spam@TEAMproject01 at -Remove-hotmail.com asks: " hi, has anyone done a project using the pic16F877 for a universal remote control." +

Interested:

Comments:

• dead link: bubblesoftonline is now a domain squatter.+

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