Don Lancaster's RESOURCE BIN number twenty-five Essential homebrew test equipment. ur usual reminder here that the power is connected, or for any quick current and thus multiplies the meter Resource Bin is now a two-way check of primary fuses, switches, line reading. Any perfect ammeter should O column. You can get tech help, cords and such. offer a zero resistance to your outside consultant referrals and off-the-wall Hint: If you place your neon tester circuit under test. networking on nearly any electronic, across a fuse in a powered circuit, the To measure voltage, a high value tinaja questing, personal publishing, lamp will light if the fuse is blown, and resistor gets placed in series with the money machine, or computer topic by vice versa. Similarly, the lamp lights meter terminals. This resistor makes calling me at (520) 428-4073 weekdays on any open switch and does nothing use of Ohm's law to convert voltage 8-5 MST. I've got a free pair of insider on a closed one. to a current. The microammeter then secret resources brochures waiting for Another tip: Some older electronic measures your current. A voltmeter you when you call or write. gear (especially tube table radios) tied should present a very high resistance A portion of my PSRT RoundTable one side of their chassis to the power to your circuit. Ideally infinite. on GEnie has also been set aside for line. Which can create a deadly shock It's just not possible for you to ever you Nuts & Volts readers. This is the hazard for the unwary. Simply hold measure anything without disturbing place to go for instant tech answers. on to one terminal of your neon tester what is being measured. For even if Among the many files in our library, and touch the other one to the chassis. you could reduce any power removed you will find complete reprints and If the lamp dimly lights, you've got a from your test to a bare minimum, the preprints for all of my Resource Bin hot chassis. very fact that information is getting columns. I've just added a new "fast extracted from an environment means access" feature for you. Have your Multimeters that the entropy is unavoidably modem dial (800) 638-8369, followed The second most important piece of getting altered. Thus, all measuring by HHH. Then XTX99005,SCRIPT. homebrew test gear is some method systems must in some manner both By the way, be sure to enter your to measure ac or dc voltage, current, disturb and distort what's being HHH immediately after your modem or resistance. The traditional way to measured. software reports a connection. This is do this is with any meter-style VOM The trick is to make your errors as how GEnie recognizes your baud rate. analog multimeter. The newer way is to low as possible. Traditional analog If you get gibberish on the screen, you use a DMM or digital multimeter. multimeters are usually said to have a were too slow with your HHH. Yeah, digital multimeters are more voltmeter sensitivity of so many Ohms A free GEnie brochure if you voice accurate and load your circuits a lot per volt. One popular value here is call (800) 638-9636. less. And they don't really cost that 50,000 Ohms per volt. A reminder that all of the previous much more. But I still feel you should To find the actual loading on any Resource Bin columns are offered both start off with a plain Jane analog VOM scale, you multiply the Ohms per volt online and as bound volumes. I have instead. Analog can put you closer to times your full scale setting selected. also just done a major update to my Ferinstance, if you are on a 5 volt DC free insider secrets mailer. Give me a range and have a 50,000 Ohms per helpline call or see my Synergetics ad NEXT MONTH: Don looks at volt sensitivity, you'll end up with a for more details. ongoing happenings in the resistance of 250,000 Ohms loading This month, I'd thought we might pseudoscience industry. your circuit being measured. take a close look at what is and is not The loading of analog multimeters useful in the area of electronic test was first eased by going to external equipment. Let's start off with¼ what you're actually doing. The meter amplifiers, first as VTVM's, and later pointer position is more ergometric. as FET voltmeters. Typical premium Neon Test Lamps And there's fewer rude surprises in multimeter circuits include amplifiers At one time, this was by far your not really measuring what you think that produce extremely light circuit most important piece of homebrew you are. Especially at first. loading. A fixed value of 10 megohms test gear. I'll still call it number one At any rate, the heart of any analog or higher is common. because of its cost and utility. multimeter is a microammeter. To Resistance is usually measured by A neon test lamp lights to verify the measure higher currents, a low value setting a current and then measuring presence of higher voltages. Which is shunt resistor gets placed across the the voltage drop that current creates great to find out whether 110 volt ac meter. This shunt diverts most of the in your resistor being tested. Older February 1994 / Nuts & Volts Magazine 24 multimeters applied a battery and a adjustments or meters that let you see new from series resistor to give you the needed your current being used. current. This is why the Ohms scales Be sure to read all the fine print on DON LANCASTER are so cramped on many meters. By these. Some are simply transformers. ACTIVE FILTER COOKBOOK the way, the series resistance will be Some are unregulated. And others do The sixteenth (!) printing of Don's bible on analog op-amp lowpass, bandpass, and highpass active the resistance value at the exact middle offer full regulation. Very few can be filters. De-mystified instant designs. $24.50 of the scale being used. used beyond their ratings. The currents used to measure low For quick and dirty work, several CMOS AND TTL COOKBOOKS Ohms can end up quite high. So high plain old batteries can be handy. Only Millions of copies in print worldwide. THE two books for digital integrated circuit fundamentals. that they can cause damage. A good these are not at all regulated and not About as hands-on as you can get. $24.50 each. rule is to never test a solid state device on protected against overloads. They also the lowest Ohms scale! run down when you least want them INCREDIBLE SECRET Always use the next higher range. to. Maxim does sell some interesting MONEY MACHINE II Better multimeters use true current regulator kits that work well with low Updated 2nd edition of Don's classic on setting sources and internal amplification to voltage battery supplies. up your own technical or craft venture. $18.50 linearly measure the resistance values. Do not forget that a shorted Nicad This ends up safer and much lower in battery can explode! LANCASTER CLASSICS LIBRARY Don's best early stuff at a bargain price. Includes power. For low resistances, brief pulse Another ploy is to combine a plastic the CMOS Cookbook, The TTL Cookbook, Active Filter Cookbook, PostScript video, Case Against techniques get used. case with several power supplies and Patents, Incredible Secret Money Machine II, and Once again, I suggest you start off a breadboarding area. Again, you'll Hardware Hacker II reprints. $119.50 with an analog multimeter. You can find ads for these here in Nuts & Volts. always add a DMM later as the need Your classic supplier for this sort of LOTS OF OTHER GOODIES ......................................Ask the Guru I or II or III $24.50 arises. Avoid the junkiest of low end thing, of course, is Heathkit. Who do ......................................Hardware Hacker II or III $24.50 meters since they are both inaccurate continue to supply these and similar ......................................Micro Cookbook I $19.50 ......................................PostScript Beginner Stuff $39.50 and rather unpleasant to use. Those industrial education products. By the ......................................PostScript Show and Tell $39.50 ......................................Intro to PostScript Video $39.50 medium quality ones from Radio Shack way, one great source for precut wires ......................................PostScript Reference II $29.50 ......................................PostScript Tutorial/Cookbook $18.50 (such as a #22-214) seem a good deal, is Squires Electronics. ......................................PostScript by Example $29.50 especially when they go on sale. ......................................Understanding PS Programming $29.50 ......................................PostScript: A Visual Approach $22.50 My first choice in an analog meter An Oscilloscope ......................................PostScript Program Design $24.50 ......................................Thinking in PostScript $22.50 is still that good old Triplett 310. This A decent oscilloscope is absolutely ......................................LaserWriter Reference $19.50 one is quite compact and has lots of essential for more serious electronic ......................................Type 1 Font Format $15.50 ......................................Acrobat Reference $24.50 accessories such as belt pouches and work. A scope lets you see the actual ......................................Whole works (all PostScript) $350.00 ......................................PostScript Secrets Brochure FREE clamp-on-ammeters. waveforms as they happen. ......................................Hacking Secrets Brochure FREE In its most common setup, a scope Power Supplies graphically plots one or more varying POSTSCRIPT SECRETS Next, you will need several power voltages vertically, while showing A Book/Disk combination crammed full of free fonts, insider resources, utilities, publications, supplies for your experiments. Most time along its horizontal axis. You can workarounds, fontgrabbing, more. For most any digital projects need +5 volts dc.