Aux input (voltage to input) Megajolt v4 jr

[pickle]

Hiya guys, great site!

I have a metro turbo engine, I am planning on using the engine coolant temp for the aux input on my v4 jr. The coolant sensor is 12v, will I have to try to reduce the voltage before it reaches the mj or is the mj regulated inside somwhere??

i have searched but cant find this out!

Any help greatly appreciated,

Thanks, Rich

[BRUCEROE]

The MJLJ has an internal 2.2K pullup resistor to internal 5V. It can be calibrated to use a standard EFI temperature sensor. Is your present sensor already in use in the car; sensors don't have an internal voltage? Adding another might be the easiest. Bruce Roe

[brentp]

Hi Rich,

What type of temperature sensor do you have? Almost all temperature sensors are passive 1 or 2 wire type. with the one wire type the 2nd wire is the body of the sensor, which is grounded. 2 wire types have the 2nd wire grounded as well- preferably to the same location where the sensing unit (i.e. megajolt) is grounded.

Here's the installation guide which illustrates how to wire the sensor.

http://www.autosportlabs.net/MJLJ_V4_ve ... e_resistor

[pickle]

Hi guys, cheers for replies, I have a one wire type sensor and it is already in use, its powered down from 12v to 10v by a voltage regulator (thats what I meant by 12v sensor)
So would it be ok if I connect the aux input wire to the temp sensor aswell like below?

Thanks, Rich

[BRUCEROE]

That would NOT be OK, for a couple of reasons. The 2.2K resistor in the MKLJ would throw off your present circuit. Even if the 2.2K were disconnected, it is likely your present circuit sometimes exceeds 5 volts at the sensor. The MJLJ can't be calibrated outside of 0 to 5 volts. But connecting a second EFI style temp sensor to the MJLJ would solve the problem. You would still need to enter a calibration chart into the MJLJ for a degrees readout, but I have made one available for degrees F. Bruce Roe

[pickle]

Thats what I wasnt sure about. I'll plumb in another water temp sensor somewhere and put the megajolt to that.. If I find that the sensor in the pic above does only recieve 5v max from the gauge I could still use it then couldnt I? but oly if it revieves 5v MAX!!

At the moment my aux input temp gauge is shownig the ADC value as the temp reading, by recalibrating it, you mean change the ADC value to degrees F or C so it shows as the degrees equilavant of the voltage reading on the gauge instead of the current ADC value? Whats the scaled value section for?

Is there a link to the one you have available in degrees F?

Thanks Rich

[brentp]

As Bruce indicated has supplied us a calibrated temperature file for the GM sensor (thanks!) I have yet to add it to the wiki (on the list!) Bruce, could you attach it to this thread?

[BRUCEROE]

If you use your present sensor (which NEVER exceeds 5V), you will have to measure the voltage and temperature (trust your original gauge?) over the operating range. Then make a conversion table for the MJLJ. Without a conversion chart the MJLJ gauge will apparently be reading backward. And disconnect the 2.2K resistor.

This is quite a project, that's why I suggest just simply adding a standard sensor & loading an existing table. I'll need to look up the sensor data sheet, from which I did a conversion chart. The sensor isn't linear with temperature, but resistance vs temp is on its data sheet. The resulting voltage with 5V applied to the 2.2K resistor can be calculated. Those voltages then make a table that the MJLJ translates from voltage input to degrees F at the on screen gauge. Guess you could do degrees C, but I believe the range of the readout is presently limited to 0 to 255. Bruce

[pickle]

Ok thanks, i'll add another standard sensor for the mj. Lookin forword to seeing the data sheet,

Thanks, Rich

[BRUCEROE]

Here is the generic temp sensor with resistance every 5 deg C; thats every 9 deg F. I figured the voltage with a 5V source through the MJLJ 2200 ohm series resistor every 9 deg F, extrapolated between. Below is MJLJ conversion table. Bruce Roe

http://www.pe-ltd.com/Downloads%5Ccoolant_temp.pdf


255
255
255
255
255
255
255
255
255
255
255
250
245
240
235
230
225
221
217
213
210
207
204
201
198
195
193
190
188
186
184
182
180
178
176
175
173
172
170
168
166
165
164
162
161
159
158
157
155
154
152
151
149
148
147
146
145
143
142
141
140
139
138
137
136
135
134
133
132
131
130
129
128
127
126
125
125
124
123
122
121
120
119
119
118
117
116
116
115
114
113
113
112
111
111
110
109
108
107
106
106
105
104
104
103
102
102
101
100
99
99
98
97
97
96
95
95
94
93
93
92
91
90
90
89
89
88
88
87
87
86
85
85
84
83
83
82
81
81
80
79
79
78
78
77
76
76
75
74
74
73
72
72
71
70
70
69
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68
67
66
66
65
64
64
63
62
62
61
60
59
59
58
57
57
56
55
55
54
53
53
52
51
51
50
49
48
48
47
46
46
45
44
43
43
42
42
41
40
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
12
11
10
9
7
6
4
2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

[BRUCEROE]

If I had your email, I could send the conversion table as a .txt
file. For some reason, my APPLE doesn't like to deal with .txt
files. Or brentp can make it available.

Here is my translation from temperature degrees F to
voltage into MJLJ, with a 2200 ohm pullup resistor to 5.00V.
This circuit is shown on the sensor data sheet. It is best
to bring both sensor leads directly to the MJLJ. Grounding
the sensor to the block can introduce ground loop errors.

degC degF ohms volts
-40 -40 102,122 4.896
-35 -31 73,340 4.854
-30 -22 53,249 4.802
-25 -13 39,064 4.733
-20 -4 28,939 4.647
-15 5 21,637 4.539
-10 14 16,321 4.406
-5 23 12,413 4.247
0 32 9516 4.061
5 41 7354 3.849
10 50 5728 3.613
15 59 4496 3.357
20 68 3555 3.089
25 77 2830 2.813
30 86 2268 2.538
35 95 1828 2.269
40 104 1483 2.013
45 113 1210 1.774
50 122 992 1.554
55 131 819 1.356
60 140 679 1.179
65 149 566 1.023
70 158 475 0.888
75 167 400 0.769
80 176 338 0.666
85 185 287 0.577
90 194 244.8 0.501
95 203 209.7 0.435
100 212 180.3 0.379
105 221 155.6 0.330
110 230 134.7 0.288
115 239 117.1 0.253
120 248 102.2 0.222
125 257 89.4 0.195
130 266 78.5 0.172
135 275 69.1 0.152
140 284 61.1 0.135
145 293 54.1 0.120
150 302 48.1 0.107

Since the MJLJ currently can only display numbers between 0
and 255, the conversion table must be limited to that range.
I just extrapolated the in between degree F values. A translation
table for degrees C will only be able to go down to water freezing.
Bruce Roe

[pickle]

Thanks BRUCEROE,

I will use your translation and add my own extrapolated values in between..
I will update this and let you know how it goes when I get a chance to do the chart and get on my mj and fiddle.

Thank you loads and loads

Rich

[alhbln]

That would NOT be OK, for a couple of reasons. The 2.2K resistor in the MKLJ would throw off your present circuit. Even if the 2.2K were disconnected, it is likely your present circuit sometimes exceeds 5 volts at the sensor. The MJLJ can't be calibrated outside of 0 to 5 volts. But connecting a second EFI style temp sensor to the MJLJ would solve the problem. You would still need to enter a calibration chart into the MJLJ for a degrees readout, but I have made one available for degrees F. Bruce Roe

How about adding a simple high resistance voltage divider (e.g. 14K/10K) to the Megajolts Aux input, which lowers the output from the temperature sensor to a safe 0-5V TTL signal? That shouldnt interfere with the Temperature Gauge (at least not more than 5-10%, which you wouldn't notice on the 240Z gauge anyway) and you could leave the factory temperature sensor and gauge in place.

[BRUCEROE]

That will work. But then there is still the problem of generating a calibration chart for the original gauge-sensor combination, how do you do that? Also, 12V to the gauge varies a lot from say, idle with lights on, to full speed no load. That voltage variation will cause the MJLJ gauge to change every time you step on the gas, because the MJLJ reference voltage is fixed. The original gauge probably has compensating circuitry.

A divider with high enough impedance to not affect the original circuit, will not be able to drive much voltage into the 2.2K MJLJ pullup resistor. So the 2.2K will need to be disconnected for decent resolution. Not needed for separate sensor.

Bruce Roe

[alhbln]

That will work. But then there is still the problem of generating a calibration chart for the original gauge-sensor combination, how do you do that? Also, 12V to the gauge varies a lot from say, idle with lights on, to full speed no load. That voltage variation will cause the MJLJ gauge to change every time you step on the gas, because the MJLJ reference voltage is fixed. The original gauge probably has compensating circuitry.

A divider with high enough impedance to not affect the original circuit, will not be able to drive much voltage into the 2.2K MJLJ pullup resistor. So the 2.2K will need to be disconnected for decent resolution. Not needed for separate sensor.

Bruce Roe

Voltage variation is a good point, i am just trying to avoid to drill a hole in my engine block. I guess i'll have a look at the gauge itself, there might be a chance to get a voltage output after the line regulator.

Good input, thanks!