14 April 2020 at 11:55 #8081
Dear Electrofriends, I have a problem that has been driving me crazy for a few days. I repeat old age looms.
Then: give one 7493 (binary counter) with external clock I obtain from the pins QA / QD a binary value with which I am going to drive a decoder. This sequence is stopped when the QD / QC pins are both a 1 logical (12^ boost) and are connected to the two reset inputs of the chip itself. (Logical AND inputs).
No problem but when the chip (with clock stopped) is powered QA / QD outputs are NOT set to ZERO but take random values.
I would therefore like to reset this chip with a pulse provided by a PIN (arduino) and put to 1 logical. I then made a table of truth to verify the conditions.
QD QC RS U
QC / QD are the counting pins,
RS the manual reset pin.
U is the output that is connected to the two reset pins of the chip:
0 0 0 0 Normal count
0 1 0 0 the same
1 0 0 0 the same
1 1 0 0 Reset to 12 ^ impulse
0 0 1 1 Manual reset
0 1 1 1 the same
1 0 1 1 the same
1 1 1 1 the same
E’ can solve this problem without having to use other additional chips (tipo AND/NAD/OR/NOR ecc) ???
Thank you for your attention
gvsoft14 April 2020 at 13:08 #8084
I don't know if I understand the problem!!
As far as I understand, you have the problem that when the power is turned on, it is positioned in a random condition.
You could do a power-on reset with very few components, also the same circuit allows you to control the reset from Arduino with just one pin
see source fidocadj Zoom fidocad
When it has finished its function, the input terminal remains stable at logical ZERO but nothing prevents you from injecting a UNO level from Arduino without breaking anything, the capacitor now charged to the limit is discharged by prolonging the reset pulse while Arduino sees the 10K resistance as output load, value that falls within the absorption limits of Arduino. From the theoretical accounts the reset fear is around 4mS, just give Arduino more time before starting its operations and it will find the integrated reset.14 April 2020 at 16:37 #8087
There are 3 diodes I seem to understand on your circuit that they connect to R1 and R2 reset pins of the 7493.
But on R1 and R2 also QD and QC of weight must be connected respectively 8 e 4 to reset the 7493 on the twelfth impulse;
This reset will be automatic at sketch runtime, while in the setup of the same sketch the reset is driven by an Arduino pin.
The scheme you propose may be fine but the connections of QD and QC on R1 and R2 downstream of the diodes do not give interference problems ??
Unfortunately for some circuits I am ignorant !!!
giovanni14 April 2020 at 17:21 #8089
They could only in particular circumstances, when a reset command arrives and QC or QD are zero, you can remedy the problem by interposing a 1k resistance between reset and assigned Q, if you have to activate the reset on 12 counting the resistances do not affect because the inputs draw minimum currents. If you need to drive a reset from arduino, the series resistor at output Q will prevent damage. It seems to me the least invasive solution and that if needed it can also be placed on the steering wheel on the weld side, that is, without remaking the printout.14 April 2020 at 17:24 #8091
I don't know what you need to reset from the program. You already know that when you switch it on it resets. However you may want to reset for program needs and then I understand this need. Not knowing the details, I leave the decision to you, I have only provided both hypotheses15 April 2020 at 11:31 #8094
Amilcare, maybe I didn't explain it well: ok the power-on reset, but the sketch I'm planning, provides for the ignition of 12 led each 5 seconds. There may be many ways to do this, but I need to use Arduino pins as little as possible (among other things, the same sketch already uses them 9 !) so the counter 7493 on the twelfth impulse you have to reset and recomic from scratch. This is why the QD / QC pins of the 7493 I have to connect them to the R1 / R2 of the chip itself. I haven't tried your circuit yet: I have to look in the drawers if there are valid diodes !!!.
thanks for now
GIovanni15 April 2020 at 11:36 #8096
Sorry Amilcare, maybe my last message is at odds with your message from 17:2i. I had only read the next one.
Ciao15 April 2020 at 12:51 #8098
1n4148 is fine I usually buy them in industrial quantities at 1 cents per piece or less. They are excellent fast diodes that you can use anywhere you don't have large voltages or large currents
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