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Playable electronic modules - modules in action

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HendriXML:
I thought I bought the TTL logic stuff looking at this website https://www.electronics-tutorials.ws/logic/logic_7.html.

I also ordered CMOS IC’s with the same gates like the TC4030BP.

On the introduction page https://www.electronics-tutorials.ws/logic/logic_1.html it says on the LS series:
74LSxx: Low Power Schottky TTL – Same as 74Sxx types but with increased internal resistances to improve power consumption. Supply voltage range: 4.75 to 5.25 volts

So I’m a bit surprised with them beeing so sensitive.

Did I buy old school stuff which is too “modern”?

I’ll add the resistors. This however will make the modules even more time consuming.  :palm:

HendriXML:

--- Quote from: Gyro on March 05, 2019, 11:36:38 am ---There are no VCC and Gnd pins on the box (aside from the PSU headers, which I assume you intend to daisy-chain). You are very likely to want to tie one or more inputs high or low when experimenting. You probably want to provide 4 pins of each.

--- End quote ---
That’s a good idea. Will add some boxes with just that, and proper symbols and all. I already have 1 module with dipswitches wich can give either high or low. A more user friendly module with larger buttons and toggle switched will follow.

Gyro:
Damn, I didn't notice from your OP that you were using bipolar 74LS series. In that case your 10k is about right, but pulled UP to 5V rather than down to GND. Bipolar LS TTL logic has very unequal high and low currents (Input : about 20uA high and 360uA low, Output: 400uA high and 8mA low).

It is much harder to pull an LS TTL input low with a resistor, you need to achieve no more than 0.8V with the 360uA input current flowing. If you pull up then you only need to get above 2.7V with 20uA flowing. If you try to use pull-down resistors then your other gates will have difficulty overcoming them with their relatively weak output high capability. Floating (unconnected) bipolar TTL inputs are an old trap, they float high on their own but are very sensitive to noise.

In the same way, if you want to drive an LED from LS TTL, then you put it (and its current limiting resistor) between the output and +5V. This means that it lights on logic low.

This may a get a bit confusing for a young mind (it made my head spin a bit just typing it!). I really suggest that you consider using CMOS 74HC logic instead. Its input current is symmetrical at <1uA (hence 100k resistor) and the outputs are also symmetrical at +/- 4mA. It is more static sensitive, but not as much as modern low voltage CMOS. Its 2 - 6V VCC and very low supply current make it much more battery friendly too.

Sorry for the confusion. I've linked a 74LS00 datasheet and 74HC00 datasheet for reference - they are representative of their respective logic family electrical parameters.

http://ecelabs.njit.edu/student_resources/datas/74ls00.pdf

http://pdf.datasheetcatalog.com/datasheet/on_semiconductor2/74HC00.PDF

HendriXML:
Thanks, you give a lot to think about. I’ll study the datasheet, but also do some measurements in pulling up/down.

Having inputs which need to pulled down is probably also handy when using comparator modules.

Battery life I’m not really concerned with yet, if some experiment is worth running for a long time it’s probably better to make a dedicated circuit for that using more optimal components. Otherwise the modules will be “in use” to much, increasing the need for more of them.

HendriXML:

--- Quote from: Gyro on March 05, 2019, 05:01:32 pm ---It is much harder to pull an LS TTL input low with a resistor, you need to achieve no more than 0.8V with the 360uA input current flowing. If you pull up then you only need to get above 2.7V with 20uA flowing.

--- End quote ---
What you say is also explained in more detail here https://www.electronics-tutorials.ws/logic/pull-up-resistor.html for those interested. The difference between pull up/down is so large, that I’m not going to measure voltage drops :-+ 15k Pull up it will be!

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