Need advice.

[Donald S. Lambert]

I grew up in an analog world and trying to learn a little about the digital world. Age 78 My first experiments in electricity were with a #6 dry cell (1.5 volts) and bell wire and nails for the core and strapping iron strips for the clapper of a buzzer. That was baack in the mid to late 1930's.<p>Now the problem. I bought a Radio Shack "electronics Learning Lab" which is powered by 6 AA batteries (6 X 1.5 = 9 volts) and it has a solderless breadboard on it plus various components that can be connected to the breadboard. And a big handfull of loose components. But the dip chips it uses are all CMOS. And I have the "The Digital Electronics Course" that was in Popular Electronics back in 1989 thru to 1991. And that course uses TTL DIPS chips which require 5VDC = or - 0.25 volts.<p>And I have two questions:<p>1. How many amps can I expect the AA batteries to supply to a 7805 regulator?<p>2. I see that a capacitor is recommended to be put on the input lead and output lead of the 7805 to take care of any spikes the TTL chips create. On the input a 2.2 uF WVDC Tantalum capacitor and on the output of the regulator an 0.1 uF disk capacitor. Is that correct?<p>Greybie

[philba]

Hi Greybie. Welcome. I an little younger than you but did a similar stuff BIC (before ICs). Wound my own motor and stuff. I think I took apart anything electrical I could get my hands on.<p>AAs typically can deliver between 900 - 1200 mA hours but dont expect to get all that in one hour. I dont recall the internal resistance of alkaline cells but don't expect much more than a couple hundred mA. Probably more than enough for your needs. <p>For a 7805 sourced by a battery, those caps will be ok. By the way, expect that regulator to really suck your batteries dry fast, even with no load on the regulator output. If you want to use a wall transformer, you'll need to increased the input side cap. Here is a formula for sizing it. http://www.circuitcellar.com/library/eq/172/1.htm
(sorry for the "other mags" url folks)<p>Now as for the cmos vs ttl. The voltage level for high and low will be different so they are tricky to mix but you should have no problem with simple combinational logic. You can run the cmos at 5 V just fine. In fact, you can run the cmos at 4.5 (3 AA cells in series) and get rid of the regulator if you want. your high and low thresholds will be slightly lower but will work just fine.

[rshayes]

Three terminal regulators have internal transistors that still have gain at several Mhz. I usually use a .1 uF ceramic capacitor on both the input and the output as close as possible to the integrated circuit. This is usually about 1/4 to 1/2 inch away.<p>I usually use a 10 uF capacitor (either aluminum or tantalum) on both the input and output. The capacitor on the input seems to increase the stability. I have had regulators oscillate when I used the minimum specified capacitor. The difference between a 2.2 uF and 10 uF capacitor is small, and if it doesn't oscillate that is one less thing to troubleshoot.<p>I usually use another 10 uF capacitor on the output. This provides a resevoir that can supply current for short periods until the feedback loop in the regulator can increase the output current.<p>I usually use a .1 ceramic capacitor for each TTL chip. This provides a local source for the transient current that most TTL circuits draw when they change state. These transients can be a fraction of an amp and several nanoseconds long. A local capacitor can supply this current and lower the effect of the power supply leads or traces, which tend to be inductive. Also use these on 555 type timers, they are as bad or worse than TTL circuits.<p>CMOS circuits are less violent, and can probably get by with less bypassing. The exception is operation at high speeds. Close bypasses will help any high speed logic family.<p>Local bypassing of the supplies for analog chips also helps reduce noise problems.<p>Buy the .1 uF ceramic capacitors in quantities of at least 25 and possibly 50. They are cheaper in quantity and you will eventually use them.<p>[ December 15, 2004: Message edited by: stephen ]</p>

[Donald S. Lambert]

Hi Philba and Stephen,
Thanks for the feed back. When I build the 5VDC circuitry I will use 10 uF capacitors.<p>The reason that I will use TTL (74XX) ics is that I have the 22 articles that Popular Electronics had, one aricle per month and they used TTL. And I have quite a bunch of TTL chips to play with. And I have had bad luck with CMOS (static electricity) and I don't have a static free place to work.<p>By the way the Radio Shack "Electronics Learning Lab" is somewhat similar to the Heathkit trainers but powered by 6 AA batteries and has a solderless breadboard on it and comes with a handfull of loose componets for the experiments. And has the advantage of not being tied to an electric outlet.<p>Greybie

[Numlock]

Hello Greybie,
Breadboards might offer you a more options than the old RS project board. Although breadboards do not offer the tightly wound steel springs that the RS experimenters' boards did, they do make things easy by allowing you to connect many wires to a single row just by pushing the wires into place. The larger versions offer up to three different power supplies on a single board.
On a side note, 1/2" Copper water pipe makes an excellent battery box for AA cell batteries. Simply cut the pipe to the length of the number of batteries that you want it to hold, solder either a pipe cap or a strip of Copper across the bottom and the housing is complete. Then add a rubber cap (found in the hardware section of most grocery stores) and poke a hole through the center to allow your 'bell wire' to penetrate. You may solder this to a spring or just twist up the wire into a sort of a ball so that pressing the cap over the pipe forces the spring or wire into direct contact with the '+' terminal of the battery inside. Solder another piece of 'bell wire' to any part of the copper tube to give you the '-' wire and you're set. I use a strip of electrical tape just to hold the rubber cap in place. I really like these because you can use double-stick Velcro to attach a 3V, 4.5V, 6V, 7.5V and 9V right to the back of the breadboard itself. (The 6V and up work better if you use multiple tubes and reverse the polarity of the batteries in the second tube.) This also affords the availability of 'spare' batteries if you are working on 'hungry' curcuits.<p>Regards

[philba]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Greybie:

The reason that I will use TTL (74XX) ics is that I have the 22 articles that Popular Electronics had, one aricle per month and they used TTL. And I have quite a bunch of TTL chips to play with. And I have had bad luck with CMOS (static electricity) and I don't have a static free place to work.<p>Greybie<hr></blockquote><p>tell me about it! I have about 10 lbs of old TTL parts - I got the sweepings from a production line years ago. Now they just gather dust because all I use is 74HC stuff. Not only did I get TTL but a huge number of 0.1 tant bypass caps and a host of random other components. <p>Use what ya got!