Help with DS18S20 Dual Temperature Meter

[mtb54703]

I purchased and assembled the DS18S20 Dual Temperature Meter from ElectronicsDIY.com (http://electronics-diy.com/pic_temperature_meter.php).

This should be rather simple project but still I'm having some problems...

1) PIC doesn't appear to run unless it's directly connected to 5v
bypassing the LM7805 (I have replaced LM7805 but with no change).  By
not run I mean that if I don't bypass the LM7805 I only a row of
rectangles on the upper line of the display.
2) No input from the second DS18S20 sensor.
3) Top line of the display shifts left and right one character (loosing first character on the line), sometimes a garbage character appears.

 

[mtb54703]

Just adding another picture...

 

[mtb54703]

Here's the instruction sheet...

 

[hobiesound]

since this is a audio electronics diy forum, i think you might be better served by the sparkfun or ladyada forums. Us audio guys rarely have to deal with temperature sensors except maybe lm35's in amps.

greetings,

Thomas

 

[JohnRoberts]

I purchased and assembled the DS18S20 Dual Temperature Meter from ElectronicsDIY.com (http://electronics-diy.com/pic_temperature_meter.php).

This should be rather simple project but still I'm having some problems...

1) PIC doesn't appear to run unless it's directly connected to 5v
bypassing the LM7805 (I have replaced LM7805 but with no change).

What voltage is at the PIC power pin with 7805 in circuit?

What voltage when bypassed?  Those PICs probably don't like a lot more than 5V

By
not run I mean that if I don't bypass the LM7805 I only a row of
rectangles on the upper line of the display.

This doesn't neccesarily mean the PIC isn't running, but it suggests the data between PIC and display is not being sent or read properly.

2) No input from the second DS18S20 sensor.
3) Top line of the display shifts left and right one character (loosing first character on the line), sometimes a garbage character appears.

Check the voltage after the 7805, should be 5V DC and no significant ripple or noise.

If you don't have a scope, use a VOM to measure 5V DC, and 0V AC with a cap in series with the VOM lead to block the DC.

IF you don't have at least a VOM, you are just guessing blindly... which isn't fun for any of us.

JR

 

[mtb54703]

Didn't realize this was an audio forum - maybe I can at least draw upon your general electronics knowledge...

Having gotten totally frustrated with his project (not to mention a bit confused) I recreated it on a breadboard.  The PIC was socketed and I had the other pieces necessary less the 10K pot, but found that 2.2K resistor provided the right amount of contrast.

Power supply is now a 12v 5Ah sealed lead acid battery.  Output is 12.44v and the output of LM7805 is 4.99v (it's also 4.99v on the leg of the PIC).  I also added a 100uF capacitor on the input side of the LM7805.  I brought it to work with me today and will hook it up to scope to check for voltage ripple when I get a chance.

Otherwise it appears to almost work on the breadboard - both sensors are giving a reading.  On the PCB I had tacked the sensors right to the headers, now there is a 4" wire between the leg of the sensor and the input pin of the PIC - I'll play with a bit and see if that really makes difference or not.  The sensors are still using parasitic power with a 1K pull up resistor - the pull ups on the PCB were suppose to be 1K but one measures at .987K  and the other at  .999K, both pull ups on the breadboard are .997K and .995K.

As for almost working - I'm still missing the character in row 1, column 1, occasionally the first line will still shift left and right one column, and it appears the PIC reboots every once in awhile since the 'splash screen' shows again on the display.

I'll update later when I can test with a scope.

 

[mtb54703]

Update...

So tonight I decided to focus on why the DS18S20s worked on the breadboard, but not on the PCB. After some careful ohming I decided there must be a short of sorts under the header for sensors on the PCB. The reading between pin 1 and pin 2 (data & ground) on sensor 1 was 4.27K Ohms (working sensor) and sensor 2 was 220 ohms (non-working sensor).

So I unsoldered the header and pulled it off. I replaced the header with 6" wires and ran them to the breadboard were I plugged into the DS18S20s. That did the trick - reading for both sensors!!

Last problem is the dropping of the first character of row one - comes and goes, causing the row to shift the left, then back to the right.

For reference, the contact page for Electronics-DIY.com lists five emails: info, sales, bulk, order & support. I've sent a couple emails to all five, but still no reply. Interestingly too, the address given for the seller on my PayPal receipt is a residential address in Flushing, NY.