0RESET0 said:I think I can follow the schematic. But I am a little confused about the switches. I know that they are creating a break between the circuit positive and the ground No they do not break the +Ve. The +5V is applied via the 4.7k resistors. When a button is pressed, it connects 0V to the line (perhaps that is what you meant by "break the positive"). For example, look at the Reset button. It is normally open so the reset line (pin 11 on the IC1 ~ 3) is held high via the resistor (this is called a "pullup resistor"). When the Reset button is pressed, it applies 0V to the reset line (a Low) so the counters are reset. but I have never seen them drawn this way. The symbol I used for the push buttons represents how the button is constructed, ie. 2 contacts that are bridged when the button is pressed. I will try to get the components and set this up next week. I have some plans this weekend that will keep me out of the house most of the time.
EDIT: Couple more questions, It looks like the transistors (No, they are integrated circuits ICs) are called out as (labelled) IC4a-d. the bottom calls out IC5 (this was a mistake, it should be IC4) as a NAND but I can't find an IC5 in the circuit. I also can't figure out where IC4b-d go in the circuit. The 74HC132 contains 4 Schmitt Trigger NAND gates but you only need one, so IC4b -d are not used. What is the purpose of connecting both inputs of these transistors to ground?
The ICs I specified are CMOS devices. Unused CMOS inputs must be connected high or low, not left floating.
You only need "tuning" if you want an exact delay. In your case, any delay greater than 10 millisecond will suffice since the contact bounce is usually finished within about 5 ms. So I chose a delay of about 50 ms so there is no need for "tuning". The actual delay will depend on the Schmitt threshold levels which can vary widely from one IC to another (look at the data sheet for the Schmitt) - but, since I've designed it for a typical delay of about 50 ms, then the delay will be greater than 10 ms for any IC.0RESET0 said:I have been reading every thing that I can find on debounce and schmitt triggers. I think I have the schmitt figured out. However, most of the things that I read about it said that there is some tuning required with the resistors. I assume that the resistor values included in the schematic are known values from past experience.
The SN7447 ICs are TTL which is (in general) not compatible with CMOS.0RESET0 said:I did pick up some things that were not on the list. I got three display drivers. The chips that I got are sn7447an. I also picked up a voltage regulator that puts out 5v. That item is part number LM340T-5.
Sean
These are called "bypass" capacitors.0RESET0 said:Something I am unsure of is the section with the ICs and the capacitors. What is the purpose of connecting the caps to the + and gnd? it does not look like they are connected to anything else. I know it it just a representation but it is a little confusing.
0RESET0 said:I have the drivers and display hooked up as best I can from the data sheets but have a couple questions.
Right now, when I turn it on and hit reset, I get three zeroes. When I hit the up button I get three eights. This is not how it should work. Correct! Trying to remedy the situation, I searched around. Using this I connected pin 5 to ground. This got me no zeroes Correct. Pin 5 is the Ripple Blanking input and is used to supperss leading zeros. I'll tel you how to do this later, as you may like to employ this function. eg. if the count is at 005, the display will show 5 and the tens & hundreds digits will be blank. but it counted up from 1 to 9 then went to gibberish. I don't know why this happened. See below. it also displayed the same thing on each digit. I needed some way to have the drivers select which digit to show. I connected the anode pins to pin 4 on the corresponding drivers. Pin 4 is the Ripple Blanking output. You don't need to use it at this stage. This got me a dimmer display that went blank on reset then counted from 1 to 9 on the first digit. Once I hit 10 I get a 1 in the tens place and a blank in the ones place (I presume this is due to the Ripple Blanking. Connect RBI to +5V or leave it open) 11 shows up fine but 12 looks like two lower case a's (I don't understand why this is happening) and it all goes down hill from there. I can see a definite pattern so I know the counter is still working. The problem has to be in the drivers of how I am connecting them to the display. Have you studied the Function Table in the 4774 data sheet? This shows how it is supposed to operate.
I have all three digits using the same seven resisters with the a-g of the drivers connected to each other then running to the resisters. This does not make sense. This may be the cause of your problems! You need 7 resistors for each display as implied in my circuit diagram.
I have changed things back to have the 3, 4, 5 pins open and connected the anodes back to 5v. I await you suggestions on this, I hate being so close to the pay off and not being able to get there my self.
Thanks for the help
Sean
ljcox said:You're welcome.
If I understand what you mean by the "7 resistor" comment above, then this is the cause your problems. But I don't see how you could connect 7 resistors when you have 3 displays not three displays, one display with three digits & 3 display drivers. You need 21 resistors.
0RESET0 said:If you refer back to the display data sheet that I linked to a while ago I could not see what link you are referring to at a quick scan. I think from memory, you're talking about the 4553 three digit BCD counter. This is not suitable for your application since you need binary outputs to drive the Tx , you will see that there are only one set of a-g pins on the display. There are three pins for the common anodes that are digit selectors. This because the IC does MULTIPLEXING which means that you only need 7 resistors. But you can't interface this counter to your Tx. I assumed that there was something inside the display that used the seven and three to make the 21. I will read thru the data sheets again and see if there is something that I missed. There has to be some out put on the driver that I can connect to one of the common anode pins so that the output from that driver goes to a certain digit. I guess I can go out and pick up three separate displays but I like the space savings of only needing 7 resisters.
Do the transistors have any numbers on them? What do they look like?0RESET0 said:Sweet, I will try to get my hands on the new parts. Would it be easier to just get three new displays, single digit type?
Yes, it would, but it is your choice.
I can probably get them at the local Radio Shack. This would mean I have to use 21 resistors but I bought that many any way.
I don't know what your Radio Shack sells, but I can buy resistor networks very cheaply at Semtronics. Semtronics sell electronic parts to industry.
They come in 2 versions, SIL & DIL. The DIL ones look like an IC. This would make it smaller for you.
I have some spare parts like capacitors and transistors. Is there a way to identify them to see if I can reuse them?
Sean
The photo shows some SIL resistor networks that have a common - the dot of the LHS. You can buy others that have individual resistors in them.0RESET0 said:I really like the idea of the resistor networks. Can you give me a part number for a dual in line type? See the photo attached and comments below. I will use the regular resistors for now so that I can play with the value to get the brightness I want.
I am going to just order three separate displays, so I won't need the other stuff any more right? Correct I will try to find some resistor networks while I am ordering the displays.
I order my stuff thru Mouser electronics at www.mouser.com
ever heard of them? Yes, I've heard of them through this forum.
I have a question about the interface with the computer. I know I am getting ahead of my self. Would it be possible to make is so that I can use the remote separately by pushing the buttons that I am using in this circuit. Then have it so that I can plug it into the parallel port and just have the "computer push the buttons"? Yes.
EDIT:
I can't get single displays from Mouser and I didn't find a resistor network that had the proper resistance. To make matters worse, if I get displays that have a different forward voltage I will not be able to use the resistors that I bought already. I don't know what they cost in the US, but they are cheap in Oz.
So, Since I did not have a chance to stop at Radio Shack today, I will stop there tomorrow and see what they have for displays.
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