DS1302 (Parallax SX52) 16x16 LED matrix scrolling clock - additional circuitry??

[tdg8934]

Thanks - I thought I would have to wait a month or so.

ALSO you mention Q3 and Q4 earlier. Do I need to get 20 of each?

Q3 is a 2N7000 N-channel MOSFET and Q4 on this particular programmer is a BS250P P-channel MOSFET. The little arrow on that center line in the symbol tells you if it's N-channel or P-channel. Both are relatively low current and come in TO-92 packages. I used this circuit on my first PIC programmer design (below).

 

[Mike - K8LH]

You're already working on collecting the 16 or 32 P-channel FDN304PZ MOSFETs, right? If so and if you think you're going to end up using a higher voltage supply for the display, then you probably want to order some 2N7000 N-channel MOSFETs. I use these so much (relay drivers, etc.) that I ordered 100 of them from DigiKey a couple years ago. They sent me ones with preformed legs on tape and when I called to explain that I ordered loose ones with straight legs they gave me a refund and told me to keep the ones they sent me by mistake.

 

[tdg8934]

Mike,

I bought some PN2907A FETs (800mA), 2.4 amp Fairchild FDN304PZ P channel FETs AND 2N7000 N-channel MOSFETs on Mouser.com too.

As a side note, I received some UDN2982A-T samples from Allegro Microsystems. These appear to be 500mA output drivers similar to the ULN2803 (but not inverted).

Can these or should these be used in the design instead of the P channel FETs.

BTW: I borrowed a new Fluke meter from work to confirm my home meter reading on the current taken the other day from my 16x16 LED matrix (display 2). I got readings from 2 mA to about 45 mA. This is not much of a draw when using a 2 A 5vdc Power Supply into Vin on the SX52 protoboard.

Thoughts about this new information...

 

[tdg8934]

Mike,

Wilf posted a new message and circuit (using a TIP32C) 3A power transistor (that I did not buy) and MORE UDN2803s.

He did say that the 5vdc 20A power supply is just about right for the voltage levels needed.

https://www.ts1000.us/cgi-bin/yabb/YaBB.pl?board=PROJIDEA;action=display;num=1176295563;start=15#15

 

[Mike - K8LH]

Well I hope the 5v supply works out. I feel very guilty about you purchasing it and our misunderstanding (I had meant cheap surplus higher voltage and higher current laptop supplies).

I wish I could have talked you into that 1/8th (12.5%) duty cycle design because I've verified that it can provide more than full brightness (grin) from a 5 volt supply.

Up to now I've only bread-boarded a couple 8x8 modules to verify hardware and software but I'm looking forward to making PCB's for a modular 8 module Clock/Calendar. Here's one idea I had (below) but it would require removing all of the modules from the aluminum frame if I had to replace a module. So instead I think I'm just going to have a single dual row 20-pin header on each module and use a 20 pin IDC cable connecting each module on the back side of the aluminum frame. The 5 volt 1.5 amp regulators on each module will be running well under their rating and should generate less heat than a big honkin' 8-10 amp regulator located somewhere else running everything.

 

[tdg8934]

Mike,

Let's see if this 5 vdc 20 amp P/S really solves the problem. No guilt should be felt. I only paid $21 and any other item including laptop bricks would be about that amount or more with shipping anyway. I checked the status of it's FEDEX shipping and it says it is 1 LB. The picture makes this thing look big but 1 LB (if true) would not be bad (just exposed more than a laptop brick). I may still get one but I want to see if this works or not using the Fairchild 2.4 Amp P channel FETs I have coming (or possibly another method). What I will initially do is remove 2 of the 2N3906 transistor rows and use the surface mounted components instead going to the 5vdc 20amp supply and using a common ground between the other 1 amp 5vdc supply on the SX52 protoboard. If the LED's look significantly brighter on those 2 rows then it was a success. I will then modify it to some variation of Wilf's or your design (which may be your 1/8th duty cycle design) - I don't know yet.

Last I built an SX48 module KIT last night (first time soldering together surface mount parts). I can use this to plug into a solderless breadboard for development without having to solder stuff to the SX48 or 52 protoboards. Very nice and compact too.

I really like the modular approach as long as the 8x8 modules line up perfectly next to each other. How do you do your PCB process?

 

[Mike - K8LH]

Can you send me a link for your SX48 kit? I'd love to see what it is you built last night. I like the idea of being able to plug it into a solderless breadboard.

Mike

 

[tdg8934]

Mike,

BTW: Here's a little bit of my background. My name is Tim Gilmore. I am 42 years old and have an electrical engineering degree from Rochester Institute of Technology (Rochester, NY). I currently work as a sub contractor (Test and Evaluation Engineer) for a division of FEMA for National Incident Management Systems (NIMS). I have always wanted to do design work but my experience after college and 10 years in the Navy brought me into Field Engineering and Test Engineering disciplines and not the Hardware design that I enjoyed in College (major: Digital Systems Design). That was 10 years ago (college). About a year and a half ago, I bought a BOE-BOT (microcontroller based robot) from Radio Shack. It had a Parallax based Basic Stamp II chip (has a PIC processor with PBASIC interpreter) and it was easy to pick up and learn. From here I have moved on to more Parallax products such as their (SX/B) Basic like instructions for their SX28 and recently their SX48 and SX52 protoboards for this particular project due to their large I/O pin count. I have been pretty loyal to Parallax and even bought their new $250 Hydra board for game development using their newest Propeller chip (8 processors called COGs - all in 1 chip). However, this Propeller chip uses a new language called SPIN that I haven't picked up fully yet. Of course it also can be programmed in Assembly. Likewise so can the SX28 (DIP 28) and SX48 and 52 (surface mount). The Basic Stamp II has more BASIC commands and a bit easier than the SX/B BASIC like language so sometimes I develop on the $50-$80 Basic Stamp II chips and then convert it over to SX/B for the $2.79 SX28/48/52 parts.

I would like to start learning PIC and AVR chips but not ready to dive into Assembly so fast. I did have some 68000, 8051, 8086, Z80 assembly programming in college but it was a long time back. I have tried learning it but got disinterested quickly because of the SX/B and PBASIC Basic like languages are so much easier to put programming together.

I have always wanted to build a moving LED display sign since college but until recently, I wasn't capable of doing it until I got my Parallax skillset up. I really enjoy visual projects including LED oscilloscopes (20 years back) and now I have a working LED moving display sign - although not perfect yet until I can drive more current through the LEDs for brightness.

So that is my up to date background so you can understand where I am comming from and why I ask so many questions.


Anyway - Here is the Parallax forum link to the SX48 OEM module that I built last night and this afternoon.

**broken link removed**

PS: I received 10 surface mount free samples today from TI (Wilf's 74HC574 chip). I wish they were DIP but I need to know how people develop their projects with these chips. I am so used to using my Parallax Professional Development Board (PDB) with DIP chips. I hate having to solder something up that may not be correct and then have to unsolder it again. In your experience what do people do with surface mount and related (Non - solderless breadboard capable parts)?

Tim

 

[Sceadwian]

Since it's what I use just download Atmel's AVRStudio, you can program ASM and simulate it without buying anything, and there is a lot of example code on the net. I wrote my first ASM code before I made my first circuit.

 

[tdg8934]

Thanks for the info Sceadwian. I will do that this weekend.

Mike,

Wilf has posted a new design utilizing the parts I have now. I just ordered some 74HC574 from Jameco (since it will be hard to use the 10 surface mounted samples I got from TI).

As I stated before - I will go with a combination design of his and yours but have to weigh everything out. Testing needs to be done first.

https://www.ts1000.us/cgi-bin/yabb/YaBB.pl?board=PROJIDEA;action=display;num=1176295563;start=17#17

PS: I am also looking at the MAX7219 - that I have working on a BASIC STAMP II last night. However, I can't get it to cascade to more MAX7219s yet.

Let me know what your thoughts are about this.

 

[tdg8934]

Another comment from Wilf and my reply:


https://www.ts1000.us/cgi-bin/yabb/YaBB.pl?board=PROJIDEA;action=display;num=1176295563;start=19#19

Tim

 

[Mike - K8LH]

Hi Tim,

Thanks for passing along your name and the nice bio'. I'm 55, a Vietnam era vet' (Army, electronic tech'), an Extra class Ham radio operator, a private pilot (wife Helen too), blah, blah, blah (grin). I'll send you more later via PM.

I caught up on your and Wilf's posts. He mentioned PWM brightness control and I remember you asked me about it before. It's really simple. Basically you drive the Output Enable lines on your driver chips (the MIC5821's in my designs) with an inverted PWM (pulse width modulation) signal that has the same period as your "scan" period. I use 1-msec interrupts for my column scan rate just like you so I set up the PIC PWM module with a 1-msec period. Then I simply modify the duty cycle register for 0% to 100% which becomes inverse brightness. If you think about it, a 50% PWM duty cycle pulse on the driver ICs output enable lines each scan period will allow the IC to drive the LEDs for 500-usecs of the 1000-usec interval. Does that make sense?

Later, Mike

 

[Mike - K8LH]

Tim,

Forgot to mention I think that little SX kit is a very clever and novel idea.

 

[tdg8934]

Mike,

It is pretty good but it's $40 inc S/H. Although Parallax sells SX48 and SX52 protoboards for $10 each + S/H but you have to solder wires to the board. I have 3 SX52 protoboards because it has 40 I/O lines and the SX48 has 36 but is virtually identical in function just 4 less RA lines (plus much smaller in size than the SX52). Soldering it to the SX48 OEM Module was quite the experience for a first time SMT solderer.

BTW: I got 10 of the SMT P-FETS from Fairchild today. I have at least 25 more coming from Mouser this week. These are extremely small so this should also be interesting to work with.

About the PWM. I like the idea and it does make sense via an interupt but how it is done, I would have to think about more as I don't know about how I can get an inverted PWM signal from the SX48 or 52. I know that Basic Stamp II's have some PWM signal so perhaps I can study this and see if I can simulate it on the SX48 or SX52.

More tommorow.

Thanks for the good bio too. I was an enlisted Navy ('83 -'92) Electronics Warfare Technician for my first 8 years and changed over to Electronics Technician title (no schooling for ET only EW) for my last 1 year and a half.

 

[Mike - K8LH]

BTW: I got 10 of the SMT P-FETS from Fairchild today. I have at least 25 more coming from Mouser this week. These are extremely small so this should also be interesting to work with.

Break out that magnifier again (grin). Actually, if you turn those little suckers about 45° you can solder them very carefully onto 0.1" spaced circuit board pads. Then use #30 Kynar wire wrap wire to wire 'em up (you'll need that silly little Radio Shack wire wrap tool too, just for the strippers).

About the PWM. I like the idea and it does make sense via an interupt but how it is done, I would have to think about more as I don't know about how I can get an inverted PWM signal from the SX48 or 52. I know that Basic Stamp II's have some PWM signal so perhaps I can study this and see if I can simulate it on the SX48 or SX52.

It's pretty much a "set 'n forget" module on the PIC and you don't invert the signal you just invert the brightness setting. A 1% PWM setting gives you 99% brightness, a 75% PWM setting gives you 25% brightness, etc. You simply stuff a new value into the duty cycle register in your MAIN when you want to change brightness settings. You don't do anything in your ISR, you simply set up the module for a 1.0-msec period and turn it on in your INIT section.

More tommorow.

Thanks for the good bio too. I was an enlisted Navy ('83 -'92) Electronics Warfare Technician for my first 8 years and changed over to Electronics Technician title (no schooling for ET only EW) for my last 1 year and a half.

Take care Tim. Mike

 

[tdg8934]

Mike,

If you look closely at Wilf's schematic, he has 1K resistors tied high going into the FDN304PZ gate. Your design does not have any resistors tied into the Gate, drain or source pins. Do you think this is necessary? I will try it when everything is ready but I wanted to hear from you about this too.

I do have plenty of the 30 guage wire and probably would have used the 45 deg angle turning. I was concerned about soldering only 30 guage wire with all of this excessive current runing through it (thinking I might have to go to 22 guage but that would be harder - but doable "I think" to work with). What are your comments?

Do you have any example of how this PWM stuff works. Is it a hardware setting on the PIC chips or an actual software command?

 

[tdg8934]

Mike,

Here is a link to another possible easier approach to this LED moving display sign using cascaded MAX7219 ICs. I have never been able to get it to cascade properly - but people (including myself) are working on it.

There are some pics too - to show you 2 of my 8x8 LED matrix modules "proper" brightness levels with no extra current or special P-FETs, etc. Just another possible option or alternative.

**broken link removed**


Tim

 

[tdg8934]

Mike,

With the help of a Parallax employee, I was able to finally cascade 2 or more MAX7219 ICs together. I had been working on this (along with many others) - me personnally over a year and a half. There was simply nothing on the internet to address this for 64 LED dot matrix displays. In my circuit:

**broken link removed**

...there are 2 MAX7219 and 2 8x8 LED matrix displays side by side (8x16 ??) and I can scroll left to right (some flickering most likely due to a higher scan rate which decreases brightness a little too but not too bad) Scrolling up is still on an 8x8 LED display so no problem there too.

It's pretty neat. I will probably make a YouTube video of it this weekend.

I am supposed to get my 5v 20A power supply today for work on this over the weekend (16x16 LED matrix project). I also got more sample parts in from TI last night. What I am finding out with free samples is that many companies limit you to surface mount parts a lot of the time which makes it harder to work with.

More later.

 

[Mike - K8LH]

Sorry for the late reply.

I've known about the MAX7219 for a few years now but never felt compelled to order samples of this 'monster' (grin). I wouldn't think cascading them would be much different from cascading the MIC5821's but again I've never played with the '7219.

I'll try to catch up on some of your questions later.

You asked about PCB software. I've used ExpressPCB with their exclusive software for three different PCB designs using their "special" 3 boards (2.5" x 3.8") for $59 deal (no solder mask or silk screen) and the boards came out great. Then I decided to try Pad2Pad with their exclusive software but haven't ordered boards yet. Neither of these produce standard gerber files that would allow you to order boards anywhere. For that please ask Bill (BlueRoom) what's he's using. I downloaded it but it wasn't very intuitive to me and I haven't gotten back to it.

Later, Mike

 

[tdg8934]

ExpressSCH

Thanks Mike.

I have been using ExpressSCH (part of the ExpressPCB package) for about a year now for my drawings. However, I have not used the ExpressPCB part yet as $60 seems a bit high for something I can solder together in a couple of nights on a protoboard with wires. Yea it's ugly underneath but until the design is perfect, I may not go with this expense. However, about 20 years ago I used the Radio Shack Etching method but the results are not as "pretty" as the professional looking boards are either. I will have to think about that for a bit.

More later.

Tim