> Going to learn a bit on eproms now...
EPROMs are easy. Much easier than Op-amps!
If you're familiar with static RAM (e.g. 61256), they are exactly the same, only you can't write to 'em without a programmer.
The basics: There are three sets of important lines. ChipSelect (CS, usually active low), A0-Ax and D0-Dy.
The A0-Ax lines are "address lines". This is your input.
The D0-Dy lines are "data lines". This is your output.
When the CS line is tied low, the chip is "selected". When it's not, the data lines are in a high-impedance state. This is really awesome, because it means you can piggy back the chips on top of each other, solder all the pins together and lift the CS lines to pick which EPROM you want to use. Actually, this is just how a memory bus works, except the CS lines are controlled by an address bus decoder (e.g. 74138) instead of a switch.
Anyhow. Okay.
So, what happens is, you provide a number on the address pins. This tells the EPROM to look up what's at that address in memory, and a few nanoseconds later, that data is on the output pins.
Wicked, eh?
This is exactly how microprocessor memory works at the simplest level. Not really hard. The only difference with what you're doing is that the EPROM is encoding tricky logic as a look-up table full of numbers, instead of a computer program as a lookup-up table full of numbers.
When selecting EPROMs, make sure you have enough input and output pins, or you will have to build extra glue logic. PITA.
I just realized, you don't need a 27512 like I was thinking yesterday. You need four bits of output per Nixie, and (as discussed earlier), eight bits of input. So, a 2764 would do the trick. Actually, an even smaller chip would do the trick, see what you have hanging around on old XT motherboards, etc.
Here's a sample pinout for the 2764:
/CE in this case is "Chip Enable", the / (or bar) over the CE indicates that it is active low. OE is "Output Enable". Together they function as the "chip select" I described above. I think they separate them for power savings/turn on time features.
Warning: it's been at least a decade since I've done this stuff, my memory could be faulty.
Wes
EPROMs are easy. Much easier than Op-amps!
If you're familiar with static RAM (e.g. 61256), they are exactly the same, only you can't write to 'em without a programmer.
The basics: There are three sets of important lines. ChipSelect (CS, usually active low), A0-Ax and D0-Dy.
The A0-Ax lines are "address lines". This is your input.
The D0-Dy lines are "data lines". This is your output.
When the CS line is tied low, the chip is "selected". When it's not, the data lines are in a high-impedance state. This is really awesome, because it means you can piggy back the chips on top of each other, solder all the pins together and lift the CS lines to pick which EPROM you want to use. Actually, this is just how a memory bus works, except the CS lines are controlled by an address bus decoder (e.g. 74138) instead of a switch.
Anyhow. Okay.
So, what happens is, you provide a number on the address pins. This tells the EPROM to look up what's at that address in memory, and a few nanoseconds later, that data is on the output pins.
Wicked, eh?
This is exactly how microprocessor memory works at the simplest level. Not really hard. The only difference with what you're doing is that the EPROM is encoding tricky logic as a look-up table full of numbers, instead of a computer program as a lookup-up table full of numbers.
When selecting EPROMs, make sure you have enough input and output pins, or you will have to build extra glue logic. PITA.
I just realized, you don't need a 27512 like I was thinking yesterday. You need four bits of output per Nixie, and (as discussed earlier), eight bits of input. So, a 2764 would do the trick. Actually, an even smaller chip would do the trick, see what you have hanging around on old XT motherboards, etc.
Here's a sample pinout for the 2764:
Code:
2764
+--------\/--------+
1 -|Vpp Vcc|- 28
2 -|A12 /pgm|- 27
3 -|A7 nc|- 26
4 -|A6 A8|- 25
5 -|A5 A9|- 24
6 -|A4 A11|- 23
7 -|A3 /OE|- 22
8 -|A2 A10|- 21
9 -|A1 /CE|- 20
10 -|A0 D7|- 19
11 -|D0 D6|- 18
12 -|D1 D5|- 17
13 -|D2 D4|- 16
14 -|gnd D3|- 15
+------------------+/CE in this case is "Chip Enable", the / (or bar) over the CE indicates that it is active low. OE is "Output Enable". Together they function as the "chip select" I described above. I think they separate them for power savings/turn on time features.
Warning: it's been at least a decade since I've done this stuff, my memory could be faulty.
Wes
Wes, pardon my complete ignorance, but how do i interface a 3-wire chip (DS1620( to a parallel bus one(2764)?
What i could do is interface the LM35 to a 0808 adc and then to the eprom...hmmm
From what i can see, it would be doable with the chip Moamps refered to from Conrad, using the eprom as decoder and a bit of multiplexing.
What i could do is interface the LM35 to a 0808 adc and then to the eprom...hmmm
From what i can see, it would be doable with the chip Moamps refered to from Conrad, using the eprom as decoder and a bit of multiplexing.
New circuit for thermometer
Here's a link to the new schematic.
The opamp amplifies the signal from LM35, giving us a 0 to 5V range for a 0ºC to 40ºC temperature differential, instead of 0 to 400mV.
This is then sampled by the ADC at a rate of 8,5KHz (i know, probably an overkill) and sent to the 28C64 EEPROM (easier to program by hand at home
). This in turn outputs 2 BCD codes (one for units and the other for tens).
I have put solder pads for the outputs as this permits to add Nixie or 7-seg displays.
Also, by switching between A7 and A8(this would have to be done manually as i made no provision on the schematic for this), the display could have it's output in ºF.
Opinions!
Here's a link to the new schematic.
The opamp amplifies the signal from LM35, giving us a 0 to 5V range for a 0ºC to 40ºC temperature differential, instead of 0 to 400mV.
This is then sampled by the ADC at a rate of 8,5KHz (i know, probably an overkill) and sent to the 28C64 EEPROM (easier to program by hand at home
). This in turn outputs 2 BCD codes (one for units and the other for tens).I have put solder pads for the outputs as this permits to add Nixie or 7-seg displays.
Also, by switching between A7 and A8(this would have to be done manually as i made no provision on the schematic for this), the display could have it's output in ºF.
An externally hosted image should be here but it was not working when we last tested it.
Opinions!
Hey, Simpleton!
Sorry, I forgot that the Dallas part was a three-wire interface. Argh. You need a serial to parallel shift register, a clock source and a bunch more hardware to get that to work right. Not worth it - red herring.
The LM35 plus an 8-bit ADC will work in its place.
Actually, if you were very careful, you could probably replace the LM35 with an NTC thermistor. And, of course, program new values in the EPROM....
The LM35 would probably be way more accurate, though.
Wes
Sorry, I forgot that the Dallas part was a three-wire interface. Argh. You need a serial to parallel shift register, a clock source and a bunch more hardware to get that to work right. Not worth it - red herring.
The LM35 plus an 8-bit ADC will work in its place.
Actually, if you were very careful, you could probably replace the LM35 with an NTC thermistor. And, of course, program new values in the EPROM....
The LM35 would probably be way more accurate, though.
Wes
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